Relaying my patio on dry mix?

How long to hydrolyze the dry mix depends on how much humidity there is in the air. It could take several days. If you want to prevent cracking (re yr other question) it should be more like 200 mm thick, with welded wire mesh (WWM) reinforcing, and on a firm soil base at that. Anything less and it will crack and there is no kind of grout that is going to stop it.