Having trobule working with Date

Hi

Can someone plz help me

I am currently working on a project in school. It is about Facebook data and I need your help.

My task is to find the respond time to questions people ask a specific organization on Facebook. I have the date when the question is posted (Posted column) and when the question is answered (Responds column).

Here is my problem:

Opining hours for the organization are from 09:00 to 17:00 and that gives me some problems:

1) Questions posted out of opining hours for example: 15-03-2015 20:48 shall be rounded to 16-03-2015 09:00 so the personal has a chance of answering.
2) Questions posted on weekends shall be rounded to first Monday at 09:00 o'clock.
3) When 1 and 2 are complete the responds time for each post shall be calculated. (1 and 2 is what i really struggle with)

Anyone up for the challenge? Would really mean a lot to me.