I don't have a good answer for you. Some say it keeps for months to a year. I've never used anything older than about 6 months, and you know how crosses go. Sometimes they take, sometimes they don't.
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~Royal
"It does not require a majority to prevail, but rather an irate, tireless minority keen to set brush fires in people's minds." - Samuel Adams
Advice given to me from a well known hybridizer, phalaenopsis pollen does not keep at all. He suggests making a cross from the pollen donor to the pod recipient when both blooms are between 24 and 48 hours of having opened. When giving me pollen he gives the whole bloom and advises to use it as soon as I get to the pod bloom. By the way he prefers to not disturb the pollen on the bloom receiving the pollen. Another tip is to apply a drop of enzymatic contact lens cleaner to the pollen for just 5 minutes before inserting into the bloom. No need to rinse. This softens the DNA protein coating that can inhibit the process. This is especially helpful when attempting a selfing. That is very specific procedure "for best results." I had saved a number of different phal pollenia and was sad to hear that my efforts were probably for naught. Had to try anyway but had zero "pregnancies." Otherwise for many other orchids you will find that many people store pollen about 6 months as described above. Some have reported success using pollen stored for several years. So store it only until your first opportunity to introduce it to the desired bloom. You might contact The Orchidseed Project, Aaron Hicks I believe it is.
Good Luck,
Lee