Collecting pollen from Polyantha

How open does a polyantha have to be to collect pollen. I have been collecting while one petal has openned. Is this too earley? I have very limitied experience with HT or flor. when I look at the pictures in bocks that flowers look like they are in quite expanded. I am used to working with cimmonea (sp?) that are only partly open flowers. Any experience would be greatly appriciated