It really depends on what you mean by megasession, as opinions differ on how many grafts should be extracted in one procedure.
On the basis of your avatar photo, it looks like you would only need a small procedure, but I see in your signature that you're a diffuse NW5, so you might need over 3000 grafts, potentially.
Some patients choose to concentrate on the front first and deal with the mid-scalp later. Sometimes they might even feel that the second procedure is unnecessary!