Alexice, if you have the latest version or the one just prior to that (so, version 1.00.04 or 1.00.05) the store is supposed to restock once every 4 hours. That's 4 hours your time -- but the game time is the same as your time, so in reality it's 4 hours game time as well. I usually only manage to see it restock once while I'm playing though. I still wish there was simply a store where you could pick any item you wanted whenever your peeps had the money and you wanted the item.