Day and night
A day does not last long, and the night is dark. Sleeping in a Bedroll and sleeping skips it. The clock only runs while you play.
The moon
The moon has phases. Nights are brighter around the full moon and darkest at the new moon. A new world's first nights are moonlit.
Seasons
Seasons last many hours of play. Autumn colours the trees, and winter brings snow and frozen water.
Weather
Fog, rain and thunderstorms come through every so often, and snow in the cold months. Rain weakens an uncovered Campfire. Everyone nearby sees the same lightning.
Snow and ice
Snow settles as a diggable cap on the ground and thaws when it warms up. In deep cold, still water freezes over so you can walk on it.