We'd love to see this feature as well. As our county is planning on opening in the next couple weeks, we have a lot of changes to the way we'll be operating things, and it's difficult enough making sure everyone knows the new system. We'd love it if we could only allow returning clients for the next few months while we iron things out.

I think one way to accomplish this would be an option to make clients enter their contact information before revealing the schedule, and if their number isn't already in the system, display a message stating that the establishment isn't currently accepting new customers.