Aurélie tells me there is no specific lesson on when to use nuit and soir.
Normally 'nuit' is night and 'soir' is evening.
'Nuit' is associated with dark and sleeping so you will say, Bonne Nuit! to someone only before you go to bed wishing them to have a good night sleep.
You will say 'bonsoir!' to someone you greet in the evening.
In the examples you mention, the first one is definitely 'nuit' as it involves sleeping or lack of. I guess the second one is more vague so it could be either depending on the context.
Hope this helps!
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