calculate hours between two dates

Hi ,
I am looking for your help for a formula which can calculate hours between two dates, as I have in sample file in cell A2 is the date n time when we have recd the order and cell B2 contains the date n time when we have closed the order what I am looking to calculate is; in how many working hours we have completed the order as per our shift timings which is Monday to Friday 5.00 PM to 2.30 AM