Certainly a rule of thumb I go by too.Anyting over 70% yellow remove. It will just increase the chance of mold.
This is what I do. I grab a blade and pull ever so slightly, if it pops off it is done, if it doesnt I leave it til it falls off. Whats the rush if its going to fall off anyway? Let the plant suck it dry.i push on the stem lightly and if it falls off it falls off and if it don`t fall off i leave it alone. don`t know if it`s right or wrong but it`s what i do.