Automated Time Calcs for Production - W/E problem

Hiya,

I'm trying to create a time calculation based on the number of hours. Our production plan accumulates time spent in manufacturing so that we can calculate when the production is due to end. I can add the ours with no problem, and have set it up to bypass from close of production at 16:30 and to start again the next day at a given time. Production will always start on a Monday at 06:30, so thats bit is fine; the problem I'm having is to make the calculation ignore weekends, and just go straight from Friday to Monday.

Any ideas? Tried using TEXT function to pick out Saturdays and Sundays, and then IF function to validate, but trips up after first amendment.

Any help/ideas would be appreciated - I've attached where I've gotten to so far