The whole process can be over in done in a couple of hours, usually much less. (1) Purchase ticket (2) Wait for e-ticket to arrive. They've speeded this up recently. You'll get two e-mails, one for the reservation pending and one with the actual ticket. Wait until the actual ticket arrives. (3) Go to your itineraries and find the reservation (3) Purchase whatever Accelerator combination you want (4) Your purchase is confirmed immediately by e-mail (5) Log out of your account and then log back in to see if Accelerator miles have posted, which is usually immediately. (6) If they have, cancel reservation.

UA has your money and is happy. You have your miles and are happy.