Pollinating Basics: video
"Fruit begins to form within one day of blooming if the flower becomes pollinated. Summer squash fruits are usually ready to harvest within three to five days of flowering, or when the fruits are about 6 inches long." - article

After about 3 weeks of female-only zucchini flowers (6 plants), I finally have male flowers opening! Whew.. finally some pollination.. Things will go OK now. The one yellow variety (I have the name, but not with me) has produced 2 male flowers, both without pollen, but there is enough from the greens to go around. I’m a beekeeper and use “bee-sticks” to pollinate: I pick up a few freshly dead bees from in front of the hive, mount them on a toothpick, then use this to transfer the pollen. I can even pry open yesterday’s closed female flower and slip the bee in. I suspect the closed flower has something to do with maintaining humidity to allow the pollen tubes to grow, so tearing the petals off could hurt the process. - Kerry

Incomplete pollination often happens at the beginning of the season, and results in misshapen fruits that are withered at the flower end. Just discard these damaged fruits before they begin to rot. You can encourage bees to your garden by growing Phacelia or Buckwheat for improved pollination.

Open-Pollination

Farmer Cranshaw grows hundreds of heirloom pumpkins open-pollinated. Several landraces are grown open-pollinated. Results are many unique squash with a blend of characteristics from what we consider species(maxima, moschata, etc): stem and peduncle shape, fruit color size and shapes etc. The farmer then chooses which ones have the characteristic their looking for and replants the seed from those squash. Heirlooms appear to be the result of this selective breeding practice over the course of decades or centuries.