If you do not want to enter 02:00 but just 120 minutes then yoiu can either:

- format the cell(s) where you want to enter that time as [mm] and enter your time as 0:120 (unfortunately not just 120, because it will be 120 days ). It will be visible as 120 but taken to calculations as 02:00:00 (you will see it in formula bar when the cell is active).

or
- leave the cell in general format, and enter 120, but in formulas refering to that cell use F4/24/60 to have it as 0.083333 of day (1/12 of day).

I'd rather use this first method, but both will work.