Changing Date when Time goes from 11:50PM to 12:00AM

Hi...I need Excel formula for the following problem:
Cell 1 = A date
Cell 2 = A time
Cell 3 = Required Formula
Cell 4 = Calculated Time using a formula

If Cell 1 = 01/12/2012 (01 Dec 2012 - UK style), Cell 2 = 11:50PM, Cell 4 = 12:00AM then I want Cell 3 value to become 02/12/2012 (02 Dec 2012) and If Cell 4 = 11:59PM then Cell 3 should stay as Cell 1

Regards
Ben

Put this in Cell 3:

=Cell 1 + (Cell 4 = INT(Cell 4))

Substitute appropriate cell references for Cell 1 and Cell 4

Hope this helps.

Pete