'120 am' does not mean a thing, in terms of time.
However, if you mean '12;00 am' , there is no such time, because is it '12 noon' or '12 midnight'.
'am' is the Latin initials for 'Ante Meridian' / Before Noon'.
So if it is '12 noon' it is neither before nor after noon, it is exactly '12 noon'.
Similarly, if it is '12 midnight' it is neither before nor afternoon, on the previous/or following day. It is exactly halfway between the two times.
So to answer your question'
12 midnight to 8:00am is exactly 8 hours.
From 12 noon to the following day's 8;00 am it is exactly 20 hours.
On the same morning there are 3 hours from 8am to 11am
1am to 8am is 7 hours.1am to 8pm is 19 hours.1pm to 8pm is 7 hours.1pm to 8am is 19 hours.
From 8am till 11pm.
8am till 10pm
It is 24 hours.8am to 8pm = 12 hours.8pm to 8am = 12 hours.2 x 12 = 24.
14 hours
Eight hours !
11.25 hours
5 hours.
3 hours.
9 hours.
Three hours !