The key is to keep your gaskets slick and shiny black...
303 lubricates and conditions the latex with silicone.
Time is not as much of a factor as the condition of the latex regarding 303 treatment.
Your best bet is to keep an eye on the appearance of the latex gaskets, if the get dry, grippy, or turn dull or gray then it is time to condition the gaskets.
Be sure not to use anything solvent based like Armorall.
By keeping the gaskets slick and shiny black, you will ensure that they are well conditioned which will add to their longevity, but also make then easier to put on and remove since they will be less likely to grip at your skin or hair. this also putts less stress on the gaskets and makes irritation at the neck and adams apple less likely.
You should store a drytop in a cool, dry and dark spot. Hanging it in a closet covered in a plastic bag will do this and reduce Ozone exposure that also causes latex breakdown.
There should be no need to retreat gaskets during a short winter.