As for the iMac. I can not vouch for how the BTO new ones will come that have soldered in RAM (21.5"), but I am betting you will have to wait for it. I know with my 27" when I purchased it with additional RAM it was only a 15-20 minute delay at the store before it was ready to go. But RAM is easy to do on previous iMacs. But I would think you will have to wait, be it a day or so for sure but only on the 21.5".