Hi there, I posted a reply and it didn't show up. I hope it doesn't show up later lol... ok so I'm new to gardening and I have zukes and crooknecks. For me, I found that with my plants they wouldn't bloom the females until the plant itself was big or mature enough. I started my plants indoors and they've been of size now to produce fruit. I've harvested about a half-dozen zukes, but no crookneck. They seem to be fruiting a bit later and slower than the zucchini.
So from what I've seen with mine, when the plant is of mature size, the flowers on the end of fruit will begin blooming. Sometimes a female on the end of a fruit will just sit there for a few days. I guess it's just gathering up energy so if it does get pollinated, it will have the stuff it takes to grow a mature fruit. For me, the zucchini flowers were on zukes at least 3" long, and the crooknecks finally bloomed when the bulb at the base of the female flower was about the diameter of a nickel. I hand pollinate, as I don't see many bees around. I don't know about other pollinators, but since It's my first garden, it's kinda in my nature to go gung-ho about it. I'm sure if I plant next year, I'll just let them do their thing lol.
The flowers open for me in the early am, probably around 5 or 6. They stay open until about 4 or 5, and then they begin to wilt. I know many people say they're an early morning flowerer, but what I think that means is that the peak of their fertility is early. The flowers are all bright and crispy. It's obvious that they're past their prime later in the afternoon.

When you first notice your female flower, take note the date and look every day. On pumpkins, after you see the first formation of the female, 10 days or so. Good luck.
You can tell when it will open the next morning when the flower looks real yellow. You can also watch the males and the females will follow the same time frame.