I keep them in the cooler "made up" and ready to use, since we use them in daily design work... honestly, I've stored them for months, occasionally (60 days) rinsing them... they are in buckets, in water...
Interestingly, if you let them go dry in the cooler with it's humidity, they will re-soak and swell up again. I usually only keep red ready to go, since that's the color we use most, but this time of year I have orange too... I buy them in the 8oz jar, which fills a 7 gallon pail when soaked. They last forever... I do add a dash of DCD to the buckets to prevent mold...