Excel: counting times and dates during non-traditional hours
 

We have to work 12 nontraditional hours per month at my job. These are hours after 6 and any hours on the weekend. I am trying to make a spreadsheet that keeps up with people's hours and gives the running month total.

So if I put that I came in at 10 AM in one weekday cell and that I left at 8 PM in the other cell for that weekday, and I put in that I worked 9-6 in the two cells for a Saturday, I would want it to say 10 hours in the total.

How would I go about doing that?