I need to derive the duration of an event from the start & end date & time entered in 4 seperate cells:

Cell B4 = 05/10/2012
Cell C4 = 23:34
Cell D4 = 05/11/2012
Cell E4 = 4:44

I would like the resulting cell to display the duration, in this case it should be "5:10"(5 hours, 10 minutes). I tried =(CONCATENATE(D4," ",E4))-(CONCATENATE(B4," ",C4)) and formatted the cell as "Custom [hh]:mm", but that resuted in the #VALUE! error.

Thanks in advance!!!