Excluding Weekends and Holidays for SO's

We are looking to see if you could help with having SO's not take into account weekends and holidays?

When we use our actual branch plants in the SO it does not look at WE and Holidays. When we use a branch plant that is more of a place holder until we know the plant that will produce the material, we would like for those orders to exclude WE's and Holidays like the branch plants. We have been trying different setups but can't seem to get consistent results. Where are the actual calanders that are used to set these up?