Hi, Marknash99. Each case is different. Each individual's goals and expectations are also different too. Usually, if you need crown work, the procedure can be done in two sessions. If you need mostly frontal work, you may want to do it in one session.
As a good decision, waiting at least 6 months would be good if you need to treat the crown or two separate regions of the scalp. If you desire to treat the same area, waiting 12 months would be good.
Some clinics do more in-depth mapping of graft locations and densities, so the timeline for subsequent surgery may differ.