Day/Night Cycle

A clock runs at a fixed ratio to real time. Lighting and colour follow it, and other systems subscribe: shops open and close, certain creatures appear only after dark, crops grow, festivals arrive on schedule. Most games also provide a way to skip ahead by sleeping or resting, which is a quiet admission that the cycle is both an atmospheric device and an obstacle players will want to route around.

Origin Systems put a working clock into Ultima III: Exodus in 1983, when home machines could barely afford to track anything the player was not looking at. Doing so was cheap in memory and enormous in implication, because a world with its own time is a world that exists while unobserved. Tabletop and mainframe designs had tracked time before, so what changed was making it visible and consequential.

Independent time is the foundation under schedules, weather, farming and survival systems, and it remains one of the cheapest ways to make a space feel inhabited. Costs are mostly friction: night is darker and therefore harder to read, timed content can be missed entirely, and waiting is rarely interesting, so designers have spent four decades inventing ways to let players skip the thing they added.