Start Shift and an End Shift

I have a Start Shift and an End Shift time,

Start Shift = 2009/11/10 09:27:06 (GMT-6:0)
End Shift Time= 2009/11/10 15:13:03 (GMT-6:0)
eg. Total Time = 5.3 hrs

I would like to take if from this format, and calculate the total time difference. Sometimes the GMT codes may be -5:0 if that means anything. For the cell "Total Time" I only need it to have a decimal format.

Thank You all that can help.
G