If something happened, say, at 10 o'clock p.m., it happened:
1. late in the evening?
2. in the late evening?
3. (other possibilities?)

Thanks in advance and best regards.
Well, of course, if you know the time exactly, "at 10 o'clock in the evening" would be the best way to say it!

Your other choices are good (1 and 2). Other possibilities don't immediately come to mind.
3. At night?
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I f you use the word 'night', is it possible to be more accurate and say something like
1. 'early in the night'
2. 'early at night' ?
Those sound a bit unusual, Demi, but 'late at night' is common enough... at least for me.
And what would 'late at night' more or less mean? From what time to what time?
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Couldn't say. Ten p.m. is late at night for me.