Here are a couple of ideas to look in to. After the initial review questions, send the process to a user task that is assigned to a user or team that can update the appointment time. This will server as a holding place for all future appointments. If the appointment is rescheduled, claim the task from that team, change the schedule date, and submit the form. This will route the process up to the gateway and back to the holding task with the new schedule. The timer boundary event will wait until the day before the appointment and let the process go into the Day of review questions. 

The above process would have two different tasks per appointment in the waiting area. To change the schedule, you'd have to change the questions waiting task and the data waiting task. If those are two different days, that may work. Otherwise, you could consider the process below. After both the Review Questions and Review Data tasks are complete, the branches merge and go into a single holding task. You could update the appointment as many times as you'd like in the holding team, then a day before the appointment, the same to review tasks would be started.