Students canceling drop ins

We run off of a class card system for our summer schedule and it would be incredible to allow students to cancel their scheduled drop ins on their own within a certain time frame. Ex. we require a 24 hr notice to cancel a drop in, so within 24 hrs of class or whatever time frame the studio prefers, they wouldn't be able to cancel. Currently, we are having students email us to cancel and we have to cancel them manually.