Thanks Joe. I think the nonweekendhours solution should be good enough for what I need.
Yes, holidays too would be the best. But for practical purposes, excluding Sat&Sun is good enough for this particular problem.
I've solved this in the past with a time dimension table that includes columns labeling weekends and holidays. Then I can query for the count of intervals (for whatever interval size my time dimension uses) in the date range joined to time_dimension where weekday is true and holiday is false, and multiply the count by the number of hours in an interval.