Want to check if the job done (Cell C2) was on or before the deadline day (C1)

C1: 23/07/2015 (cell contains date only)
C2: 23/07/2015 01:00 (cell contains date and time)

instead of =IF(C2<=C1,”Done on time”,”Not done on time”)

Instead use:
=IF(C2<C1+1,”Done on time”,”Not done on time”)

Seems to work for me.

Have changed it from <=, to just less-than (<), but incremented the deadline by a day.