Within the ClassPass dashboard, there are three primary opportunities to communicate with your customers: the "Class Description," the "Business Profile," and the "How to Prepare" sections. The content in these three fields is included in various areas of the ClassPass site, and on reservation information sent to customers.
You should use some combination of these three opportunities to clearly communicate your policies surrounding arrival time (first timers vs repeat customers) and the ClassPass to Mariana Tek account conversion process. So long as those policies are written down and clearly communicated, ClassPass will support any resulting penalties if a ClassPass customer is denied entry to class.