Feminized pollen sacks not filling with pollen

This is my 1st attempt at using colloidal silver to make my own feminIzed seeds. I have 4 plants in a 3 x 3 tent. I sprayed 1 plant with colloidal silver & left the others alone. I’m nearly 4 weeks into flower and I’ve been spraying daily with colloidal silver (30ppm) since the flip, but very few sacks hold any pollen that I’ve seen as of yet. Some pollen sacs are even busting open but completely empty. I was able to extract some pollen last week, but I only put it on 1 cola & I’m already seeing seeds forming on buds...that was fast! It actually looks like all or most of the buds on all 4 plants are now bearing seeds, so it looks like widespread pollination occurred without my help?
How long does it take until pollen sacks are ready for extraction?
...And any other tips & tricks for making feminized seeds would be appreciated!
The plant I sprayed is Sacred Slaze (Super Lemon Haze + Krishna Kush). I have more of strain plus Gorilla Glue & White Widow in the same tent. Here are a few pics...

. the same

Looks like your doing fine to me