When's the best time?

[Bud Green]

Hey outdoor specialists!

It's been a long time since I tossed pollen...
When would you say is the best time, in bud development, to use a brush to dust on some pollen?
I have several large girls outside and they're all in different stages of bud growth...
I have some pollen stored properly in the freezer and I want to let 3 or 4 of my girls get some satisfaction..At least on 1 lower branch...
Any pics of the bud development stage ready for pollination would be helpful...

Thanks!

 

[the gnome]

plenty of nice white pistils, around 4wks sounds good to me bud