Has anyone visited this exhibit? If so, is it necessary to purchase tickets in advance?
We did. It was fabulous. I believe it's there until 7/29. My wife and I each had a list of everything we visited in Florence over 4 days and we separately rated everything. Both of us put the Cezanne exhibit #3 on our list. This was ahead of il Duomo, the Bargello and the Uffizi.
To answer your question, we walked right in. Just show up at 9:00am when it opens and you should be fine (cooler also). Tickets do not have time slots like the Accademia. In late May, it wasn't crowded (as opposed to the Accademia and Uffizi that were sold out and crowded). When you go in the ticket office, I seem to remember that the #1 counter was for advanced tickets and the #2 counter was for walk-in ticket sales. The ticket sales room is not large. You'll have to check your large bags.