Flora, I've never pressed Gerbera, but I'd wait at least 2 weeks with something I'd never tried before just to be absolutely sure they are fully dried. Or maybe have a "test" sample...leaving most undisturbed. For thick petals, you might try changing your blotter paper after a few days, but be careful as oftentimes petals may be stuck to paper. Sometimes you can bend paper slightly to free the petals, or tap lightly on the opposite side of paper, or even better wait another day or two. Then place on fresh blotter paper, cover with another sheet, and place back in your press (or under weight of some kind).

Most of us press far more than we think we might need as some do shatter or not turn out well, but once dried they will retain color for years if stored in dark (I just leave mine in old phonebook with rubberbands around it to keep tightly closed).

It's hard to describe exactly how you'll know when the material is fully dried...I just try to "curb my enthusiasm" and work on some other project for a few weeks. Good luck...josh