no need to rush, last time it took several hours after the download was published until i recived my e-mail for beta, too.
after you purchased you dont have to do anything but checking you e-mails for the beta key. it will be send to the same adress as the details about your order.
if you havent got that mail until tomorrow 12 o clock, check again this forum for information about possible problems with the mails or the beta (i dont think there will be any...) and if normaly you should have recived one, contact the support maybe or write it down here again. some of the devs also look into this forum and they will be better informed as i am about "where do i have to ask for support in that part?"
mfg
EDIT: hmpf he was faster 