Actually I just looked it up and they're more bizarre than I thought. They are actually "protogynous". Meaning all flowers start off as female and as they mature they turn male.

I should've just said "later" instead of "later in the year"

I'm not sure how long pollen stays viable in the environment. Some species can stay viable for many weeks but most are just a few days I think. They can stay viable for years if refrigerated properly however.