Day-Night Cycle

Time moves forward on its own: every 3 turns it goes from Morning to Noon to Evening to Night and back to Morning. Each period has its own atmosphere for the AI and its own music, and the player can always see what time it is. Built from behaviors, conditional lore and music rules, no code.

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What you'll build

• Four periods: Morning → Noon → Evening → Night → Morning
• Time advances every 3 turns, without the player doing anything
• The atmosphere changes: each period has a lore entry describing light, temperature and what people are doing, and only the current period's entry reaches the AI
• The music changes: birdsong in the morning, crickets at night, faded from one to the other
• The time is on screen for the player

How it works

Turn 3 ends
  → The behavior "Morning → Noon" fires (Every N turns: 3, ONLY IF Time of day is Morning)
  → It sets Time of day to Noon and tells the AI time has moved on
  → The lore entry "Noon" (condition: Time of day is Noon) now reaches the AI; "Morning" no longer does
  → The music rule for Noon matches, and the Noon track fades in
  → Time of day on the player's screen reads Noon

Only one thing changes when time moves: the variable. The lore and the music each watch the variable, so they follow by themselves.

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Step by step

Step 1: Create the variable

In the Add row at the bottom of the card, click ＋ Variable.

Field	Value
Name	Time of day
Type	Text
Starts at	Morning
Behavior Rules	The time of day: Morning, Noon, Evening or Night. Describe light, weather and people to match it.

Open What the AI does with it and set AI access to AI read-only. Behaviors move the clock; the AI only reads it.

Click Show on the player screen so the time appears on the chat page.

A new game always starts from Starts at, so the cycle begins at Morning every time; you don't need a behavior to reset it.

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Step 2: Write four period entries

Add a lore entry per period. Then drag the Time of day variable onto each entry, click the line, and set its condition: Time of day is Morning (and so on). Each entry moves into the conditional lore block and only reaches the AI while its condition holds.

Morning

[Time of day: Morning]
It's early morning. Bring this into scene descriptions:
- Soft light from the east; the air is fresh and cool
- Dew on the grass and petals catches the light
- Birds in the branches, a rooster somewhere in the distance
- People are just getting up; shops open one by one
- The mood is calm and hopeful

Noon

[Time of day: Noon]
It's midday. Bring this into scene descriptions:
- The sun is straight overhead; the ground glares white
- The air is close; distant things shimmer in the heat
- Most people rest in the shade; the streets are quieter than in the morning
- Taverns and eating houses are at their busiest, and the smell of food drifts out
- The mood is slow and sweltering

Evening

[Time of day: Evening]
It's dusk. Bring this into scene descriptions:
- The setting sun turns the sky orange and purple, clouds edged with gold
- Long shadows stretch from buildings and trees
- Birds fly home; cooking smoke rises from the rooftops
- People finish work and head home; children chase each other in the street
- The mood is warm, a little wistful

Night

[Time of day: Night]
It's deep night. Bring this into scene descriptions:
- Moon and stars are the only natural light, silvering everything
- Most windows are dark; here and there a candle still burns
- A cool breeze carries the sound of crickets and frogs
- The streets are nearly empty; a night watchman passes with a torch
- Something may be waiting in the dark: animals, thieves, or worse
- The mood is quiet and watchful

If all four reached the AI at once, it wouldn't know which to follow. The conditions make sure only the current one does.

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Step 3: Create the behaviors that move time

One behavior per step of the cycle. In the Add row, click ＋ Behavior.

Morning → Noon

Part	Setting
When it fires	Every N turns: 3
ONLY IF	Time of day is Morning
Effects	Change variable: Time of day to Noon
	Tell the AI: Time has moved on from morning to noon. Let the change show naturally in your next description.

Noon → Evening, Evening → Night, Night → Morning

The same, with the next pair of values:

Behavior	ONLY IF	Change variable	Tell the AI
Noon → Evening	Time of day is Noon	Time of day to Evening	Time has moved on from noon to evening.
Evening → Night	Time of day is Evening	Time of day to Night	Time has moved on from evening to night.
Night → Morning	Time of day is Night	Time of day to Morning	Night is over and a new day begins.

All four fire on the same turns (3, 6, 9…), but each one's ONLY IF names a different period. The engine checks all four against the time as it was before any of them ran, so exactly one of them fires each time.

Tell the AI slips the AI one line, for its next reply only. The lore entry does the lasting work; this line just makes the transition read naturally.

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Step 4 (optional): Music per period

Add four BGM tracks on the Audio page (click ＋ Audio in the Add row if the card has no audio yet): Morning, Noon, Evening, Night, each with Loop Audio on and 2 seconds of Fade In (s) and Fade Out (s).

Then open BGM Configuration → Conditional BGM → Add Conditional Rule, once per period:

Field	Value
WHEN	Variable condition: Time of day is Morning
Play	Morning
Fade In (s) / Fade Out (s)	3 / 3
Stop previous BGM	On

When the time changes, the old rule stops matching and the new one starts its track: one fades out while the other fades in. See the Audio Design Guide for more on rules.

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Step 5 (optional): A clock on screen

Show on the player screen (Step 1) already puts the time on the chat page. For something with more character, use the player interface:

• The Adventure HUD template (under Whole screen) shows the current location, day and time, and two meters. It adds its own variables for day and time of day; delete those and point its text at your Time of day, or use its variables instead of yours
• Or add a Text part to the conversation page and use Insert a variable's value… to show {Time of day}. Add Image parts for a sun and a moon, each with When to show → When a variable matches (Time of day is Night for the moon)

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Step 6: Playtest

Click Play in the top bar.

1. For the first two turns it's Morning
2. After turn 3 it's Noon, and the AI's next reply mentions the heat or the sun overhead
3. Three more turns: Evening. Three more: Night. If you added music, it changes each time
4. Three more: Morning again

This turn on the right of the playtest shows which behavior fired and which lore entries the AI got.

If something goes wrong:

Symptom	Likely cause	Fix
Time never changes	The behaviors' ONLY IF values don't match Starts at	Morning in the variable and in the condition must be spelled the same
Time jumps two periods at once	Two behaviors share the same ONLY IF value	Each behavior checks a different period
The atmosphere doesn't change	An entry's condition is wrong, or it's still in the always-sent block	Check each entry's condition and When the AI sees this
The AI changes the time itself	AI access is still AI can read & write	Set it to AI read-only
Two tracks play at once	Stop previous BGM is off	Turn it on for each period rule

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Variation: periods of different lengths

Every N turns always uses the same interval. For long days and short nights (say 4 turns per daytime period and 2 for the night), count turns yourself:

1. Add a Number variable Turns this period, starting at 0, with AI access set to Engine only (hidden from AI)
2. Add a behavior: Every turn, effect Change variable Turns this period plus 1
3. Change the four time behaviors' When it fires to Variable crosses threshold on Turns this period, Rises above: 3 for Morning → Noon, Noon → Evening and Evening → Night, and 1 for Night → Morning. Keep each one's ONLY IF on Time of day
4. Add Change variable Turns this period to 0 to each of the four, so the count starts over in the new period

Real time instead of turns

Every N seconds fires on a clock while the player has the game open. With 300 on the four behaviors, a day passes every 20 minutes of play, whether the player is typing or not.

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Custom code route: a time badge on the last message

If you write your own interface, read the variable in the interface code. Everything above stays the same.

Panels → Front End Code → open index.tsx and replace the default return <Chat />:

export default function MyWorld() {
  const api = useYumina();
  const timeOfDay = String(api.variables["Time of day"] || "Morning");

  const timeConfig = {
    "Morning": { icon: "☀️", color: "#fbbf24", bg: "rgba(251,191,36,0.15)" },
    "Noon":    { icon: "🌤️", color: "#f59e0b", bg: "rgba(245,158,11,0.15)" },
    "Evening": { icon: "🌅", color: "#f97316", bg: "rgba(249,115,22,0.15)" },
    "Night":   { icon: "🌙", color: "#818cf8", bg: "rgba(129,140,248,0.15)" },
  };
  const current = timeConfig[timeOfDay] || timeConfig["Morning"];
  const msgs = api.messages || [];

  return (
    <Chat renderBubble={(msg) => {
      const isLastMsg = msg.messageIndex === msgs.length - 1;
      return (
        <div>
          <div
            style={{ color: "#e2e8f0", lineHeight: 1.7 }}
            dangerouslySetInnerHTML={{ __html: msg.contentHtml }}
          />

          {isLastMsg && (
            <div style={{
              display: "inline-flex",
              alignItems: "center",
              gap: "6px",
              marginTop: "12px",
              padding: "4px 12px",
              background: current.bg,
              border: `1px solid ${current.color}33`,
              borderRadius: "999px",
              fontSize: "13px",
              color: current.color,
              fontWeight: "600",
            }}>
              <span style={{ fontSize: "16px" }}>{current.icon}</span>
              <span>{timeOfDay}</span>
            </div>
          )}
        </div>
      );
    }} />
  );
}

What the code does:

• api.variables["Time of day"] reads the variable by its name
• timeConfig maps each period to an icon and colours
• isLastMsg keeps the badge on the last message only. Remove that check to stamp every message with the time

The status next to the file in Panels → Front End Code should read a green OK.

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Quick reference

What you want	How to do it
Do something every N turns	When it fires: Every N turns
Do something on a real-time clock	When it fires: Every N seconds
Branch on the current value	Several behaviors with the same trigger and different ONLY IF conditions
Give the AI period-specific atmosphere	One lore entry per period with a condition on Time of day
Change music with the period	Conditional BGM, Variable condition, Stop previous BGM on
Tell the AI that time moved on	Effect: Tell the AI (next reply only)
Keep the AI from changing the time	AI access: AI read-only
Show the time	Show on the player screen, a Text part, or interface code

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This is Recipe #9

The same setup (a variable that behaviors move on a rhythm, with lore and music that follow it) works for weather, seasons, or an NPC's mood. The Daily actions template in the player interface adds a day counter, a time of day and a few actions per day, for life-sim and management cards.