When nightfall comes, it means that it's time for night to start. This means that it's time for people to go to bed and for the lights to be turned off.
It's nighttime soon, so it's time to go to bed.
The sun is setting, which means it's time for night to start.
noun
the time of day immediately following sunset
Synonyms:
1
By nightfall, the riots had spread to even the more remote parts of the island.
2
The fighting lasted until nightfall.
3
By nightfall, the scientist is himself afflicted with the nasty boils.
4
They ascend the cliffs and by nightfall come upon the nest.
5
After nightfall, the action of the main Japanese line concluded.
6
At the nightfall of the second day, the judges announced the Top 20.
7
By nightfall on June 13, the Marines were unbearably fatigued.
8
By nightfall, the Americans had occupied a portion of the fort's surface.
9
The celebration begins after nightfall on the last day of Passover.
10
By nightfall on 12 April, the Canadian Corps was in firm control of the ridge.