I believe that this formula will give you want you are looking for.
<pre>=HOUR(SUM(B1-A1)) & “:” & MINUTE(SUM(B1-A1))</pre>
This function assumes that A1 is the starting time, and that B1 is the Ending Time. You do need to make sure that Excel understands that the columns A and B are setup in the time format, and don’t have just text in there. If you need to handle overnight shifts this will need to be adjusted, but if everything is single day work without going over midnight it’ll work just fine.