Your guide will wait for your for you between the Cenacolo (museum entrance) and the Church entrance.
Il Cenacolo
15 minutes • Admission Ticket Included
Santa Maria delle Grazie
30 minutes • Admission Ticket Free
You can cancel up to 24 hours in advance of the experience for a full refund.
I recommend this tour as the guide tells you a little about the buildings and history before you go in for the viewing.