Nothing else to add, I just want to make sure.
Times of day,when expressed as digits, are, in essence, numerals, and numerals, in the words of the ‘Longman Grammar of Spoken and Written English’, ‘form a rather self-contained area of English grammar.’ Numerals aren’t nouns of any kind, because they cannot be modified in the way that nouns can be modified. We can’t speak of a nice 12:30 or the 12:30 I was looking at yesterday.
Is it breaktime yet? Every breaktime is a great time!
I can replace this with: It is 10:00 am yet? Every 10:00 am is a great 10:00 am! I call this a noun.