Working days and hours only

Thank you very much Fotis1991 for the prompt reply

So here where I stand. I took this formula and changed the work day start and end hours from

=(18/24-MOD(A1,1)+MOD(A2,1)-9/24)*24 + (NETWORKDAYS(A1,A2)-2)*9

to

=(17/24-MOD(A1,1)+MOD(A2,1)-8/24)*24 + (NETWORKDAYS(A1,A2)-2)*9

It's not giving me what i want.

* I know that NETWORKDAYS is excluding Saturdays and Sundays so I think I have to add something to change that
* The calculation should exclude anything before 8 Am and exclude anything after 5 PM

Note: A1= 07/09/2013 9:30:00 AM
A2= 13/09/2013 4:00:00 PM
The result should be 45 hours