Hi Faisal ,
A straightforward formula such as :
=NETWORKDAYS($B10+$C10,$D10+$E10,$J$2:$J$10)
will give the difference between the Start Date and Start Time ( in B10 , C10 ) and the End Date and End Time ( in D10 , E10 ). You can add 1 to the above formula if you wish.
The problem was with your value in E10 , which was not a time value ; for a proper time value , the value should be between 0 and 1 ; this value was the integer 12.
Narayan