How many hours is 120 am till 8am?

'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.