At the end of the purchase process on PayPal's web site, there's a link along the lines of "Return to www.sublimetext.com". If you click this, then you get the license key issued immediately. I realise that it's not at all obvious why you'd want to click on it, but I don't have any control over the wording, unfortunately.
While most users do indeed click on the link, for those that don't, there's usually a several hour delay till I'm able to send out the license key by hand. I do send them out as soon as I can, but given I'm in Sydney, I'm generally asleep when the purchase is made.