Military Time Not Calculating after Midnight.

Presumably actual time could be early as well as late? These questions are always difficult because of the circular nature of time (for your example 03:00 could be 19 hours early rather than 5 late), so you need to make some assumptions.

Let's assume that actual arrival time will never be more than 2 hours early (adjust as required) and use this formula for thee number of minutes late

=IF(MOD(F5-E5+"2:00",1)-"2:00">0,MOD(F5-E5,1)*1440,0)

You would need to include a date with your times, otherwise there is no way for Excel to see if 03:00 is 5 hours late, or 19 hours early. Alternatively, decide on a breaking point, for instance if it seems to be more than half a day early, then treat it as if it's late. e.g.: =MAX(F2+((F2+0.5)<E2)-E2,0)

Of course if the actual time is always after the scheduled time, you could just use: =F2+(F2<E2)-E2

Using MOD here is a simple way to cope with time periods passing through midnight.

I assume you have your result cell custom formatted as [m] - if you format as general you'll see 300....or if you want to leave the cell formatted as [m] then take out the multiplication by 1440, i.e. use

=IF(MOD(F5-E5+"2:00",1)-"2:00">0,MOD(F5-E5,1),0)