The game has 3 states of the day.
Day: with full daylight, you can see everything on the map. The most common time to do the normal things of the game.
Sunset: in the evening, fireflies start to appear, and the screen turns to an orange tint. If you're out in the Wildlands, you might consider going back to your farm!
Night: after the sun sets, you can't see anything. Use this time to sleep and recover energy.