There is a very clear article on the Gelshield process in PBO May 08.

Goes through the whole process from start to finish with pictures. It says you can apply 2 coats a day, but also that you can leave it up to 6 months between coats without any need to re-key the surface.
The only exception is that the antifouling must go on the same day as the last coat of Gelshield.

Worth reading if you are considering going down this route.