die Nachtzeit
nighttime
The period of the night, that is, the hours between dusk and dawn.
Zur Nachtzeit sind die Straßen in diesem Dorf völlig leer.
At nighttime, the streets in this village are completely empty.

nighttime
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nighttime
The period of the night, that is, the hours between dusk and dawn.
Zur Nachtzeit sind die Straßen in diesem Dorf völlig leer.
At nighttime, the streets in this village are completely empty.

The word 'Nachtzeit' (nighttime) is a simple compound made up of 'die Nacht' (night) and 'die Zeit' (time). So it literally means 'the time of the night.'
Während der Nachtzeit ist das Museum geschlossen.
During nighttime, the museum is closed.
'Nachtzeit' (nighttime) is a somewhat formal or written expression. You often find it in official notices, legal texts, or police reports.
Laut Gesetz gilt zwischen 22 Uhr und 6 Uhr die Nachtzeit.
According to the law, the nighttime period applies between 10 p.m. and 6 a.m.
This noun is very often used with the preposition 'zur' to indicate a point in time. The fixed phrase is 'zur Nachtzeit' (at nighttime).
Einbrüche ereignen sich häufig zur Nachtzeit.
Burglaries often occur at nighttime.
day
'der Tag' and 'die Nachtzeit' are opposites here. 'der Tag' means the bright part of the day, when most people are awake and working or out and about. 'die Nachtzeit' means the hours of the night, that is, the dark time between evening and morning. 'Tag' is a very normal everyday word. 'Nachtzeit' sounds a bit more precise and is often used when talking about rules, quiet hours, work, or specific times.

Während der Nachtzeit soll im Haus niemand laut Musik hören.
During nighttime, no one in the building should play loud music.
Am Tag spielen die Kinder draußen im Garten.
During the day, the children play outside in the garden.