I think it will have to be shorter for a product like Griot’s. These sprays cure fast. I tried this with Fireball Pirouette on an acrylic shower mirror and I got noticeably better (insane) hydrophobics with two layers after about 15 min. I use this mirror kind of as a test and waiting longer didn’t seem to help and made it worse, but I wasn’t able to get that same result again without polishing it for whatever reason. Pirouette is a solvent based product not water based like Griot’s so I wonder if two layers actually works better or worse because of that. It’s possible water based products don’t layer well because the carrier can’t “wet” the surface.