At least a year, if you keep it cool, dark, and DRY. I've read it can be stored even longer, but that's the longest I ever did (and then used same).
Heat up some flour, a tablespoon or two, to ensure that it is "super dry." Use it to cut your pollen up to 1:10. After it has cooled, of course. Place in a small container - the smaller, the better, as in "whatever your pollen mixture can completely fill." Make sure everything is sterile, and the same for any artist's brush / et cetera that you use to later dip out of the container with. And, again, completely dry.
The flour isn't really necessary, of course. But each one of those
tiny pollen grains can, in theory, produce one seed. I've never tried counting the little buggers, lol, but I'd guess that just the amount that could cover your little fingernail in a layer one grain thick would be capable of producing a thousand seeds, if not (many) more. IF that amount doesn't all land in one spot on a female plant. So cutting it always seemed like a really good deal to me.
A little dab will do ya. I used to keep pollen from interesting males around for when I felt like producing something a little different from a prized female or two. Shame I don't have any these days
.