time difference - conditional formatting and fix

Hi,

I have start/end cells for entering times on each days (with drop-down lists). In want to highlight end time of first day and start time of next day, if time difference between them is less than 11 hours. In my sample worksheet would that be cells C3 & D3. My current CF formula for that is :

=IF(TEXT(D3-C3+(D3<C3);"hh:mm")<"11:00";"TRUE";"FALSE")

First problem is that It only highlights one cell.

Second problem are my formulas for calculating time difference for each day ( merged cells B4 & D4, in sample). If I leave start cell empty and end cell filled, It correctly calculates. But If start cell is filled and end cell is empty, It calculates wrong

How can I fix this ?

Thanks for help !!