Calculate time different between two date:time

I need help for calculating duration between two dates:time excluding weekends. here with attached the file.
Thank you.

Open Time= 2015.06.16 15:46:44 Close Time= 2015.06.18 00:47:05 Duration= ?????
Open Time= 2015.06.12 04:01:12 Close Time=2015.06.16 08:18:39 Duration= ????? (should be deduct the weekends)

weekdays=monday 00:00:00 to friday 23:59:59
weekends=saturday 00:00:00 to sunday 23:59:59