The MAP-MSRP-Margin option will check for MAP first. If MAP is available, that will be the product price. If MAP is not available the system will look for MSRP. If MSRP is not there, it will use the wholesale price + 30%.
The updates run immediately after you save the change. The system updates each brand one by one and updates the prices. This takes a few minutes per brand so the total time depends on the number of brands selected.