Yes females only open for a few hours in the morning for one day only. In fact if you go and pry one open at the end of the day after it has closed, you'll see it's female parts have already turned black and are shriveling.

I have personally seen my males open for several days, but I don't think they work very well as time passes.

So the female flower only has a few hours to get pollinated.
Sadly this is a small window of opportunity.
Thanks

True, but if you have any bees, ants or other flying insects in the area they will be busy making sure the job gets done. If not, it is quite a simple task to do on one's own.

I read somewhere that pumpkin pollen is only 10% viable the next day and needs 1000 specks of pollen across all the female parts. I couldn't for the life of me find any other sources to back that up. But i do have a lopsided pumpkin growing.

If I know a female is going to bloom the next day, I find a male flower that is flashing it's pride for the first time, or use multiple males to increase the odds of picking a better viable pollen.