Teh only time I have done this is when I have a child that is a set part time and I can tell the family what days are available. It is then up to them to make their appointments, etc. on the days I have open. But they only pay for the days they use. I have a child that is 4 days a week and a mom that was using the odd Monday but has since just made it a regular so now she knows she has one day off a week to do whatever she needs to do.