Pollen-drying seems to me to be a delicate thing. I’ve used essentially the same method for 25 years or so but the process of shedding depends on things I can’t seem to control. I have best luck (usually) by picking the flowers on they day they should open and just laying them on a petri dish with the lid partially covering. If I have several flowers at once I skip the lid. For a single one I almost close the lid. It seems that a moderately high humidity is beneficial for the stamens to ripen. As I set these in my kitchen, it is usually drier than outside would be, except that as the season progresses it gets hotter and drier outside. Living in Kansas I experience wide swings of heat and humidity.
Getting pollen to shed from picked anthers is somewhat more difficult that from intact flowers, but if I want to make crosses both ways I don’t want to sacrifice the flower so I strip the stamens into a petri dish directly. Usually I allow a couple days for proper drying. Then by putting the lid on adh shaking back and forth I usually dislodge the pollen from its stamen. With plastic disposable dishes that I use, static electricity often leads to the pollen ending up mainly on the lid.
Because I pollinate everything with a finger, I just run a finger round on the lid, or dip into the dish 'til it holds enough and dab it onto the waiting pistils of an already prepared flower. Sometimes I have a lot of stamens from 20 or so flowers in one dish. Then I can shake the dish repeatedly and keep getting more and more pollen to shed, especially if I am working outside in the sun. It seems to ripen almost while you watch once it reaches the right stage.
However some flowers are very grudging of their pollen, even from the same cultivar on different days. That seems to be the case more often with isolated stamens than with whole cut flowers.