time 24hr

i am setting up a time sheet with start and finish times (no breaks etc just start and finish)
i have used the time cell format [00]:00 which works fine on a 24 hrs clock if the start time is lower than the finish time eg start 08:00 finish 16:00 = 8 hrs

the question i have is if i have a night shift starting 21:00 finishing 06:00 what formula do i need for this

i have attached the table i have devised

sorry if this has been asked before i have looked
thanks in advance

Try using this formula in D5 copied across

=MOD(D4-D3,1)