Many stores put a date on the tank of when they got the rock. This date will help you determine how long you have to cure it yourself, because no matter what, I think it's a good idea to cure it fully yourself as well just to be safe.
I would not trust many people. If it is a reliable source, maybe you can trust them. Otherwise, take extra precaution than usual and let it cure in your house for longer than you normally would. It can't hurt the rock, nor your tank.