Do you have to make an appointment to do an endowment session?

Depends on the day of the week- weekdays, no appointment needed

I am going to be very specific. If you are going for your own endowment. (first time ever) you need the appointment. If you want to participate in any session or ordinances no appointment need it. Just check their schedule.

Yes, you gotta call first and tell them the day when you are gonna go.

We only went once while we were visiting NYC, but we didn't have an appointment and there was plenty of space on weekday late morning session.