A student asked me a very good question: what is the difference between ‘at night’ and ‘in the night’?
It’s a good question because I never thought about this before. The best answer I can give is nothing. There is no real difference.
However ‘at night’ sounds a lot more elegant, and ‘in the night’ sounds rather clumsy.
I always like to use ‘at night’, and the only time I would use ‘in the night’ is if I am writing something like poetry or the lyrics of a song, when the three syllables of ‘in the night’ seem better than the two syllables of ‘at night’.
But I rarely write poetry, so my best advice is to always use ‘at night’.