You can level as if its a normal account. Once your payment is finalized it goes through usually takes 24 hours. I did mine on saturday morning and by sunday when I woke up my accounts where unlocked.
Its all about how long it takes for the CC payment to be verified. But when you pay it does state it can take up to 72 hours. Just gotta read the print before pressing yes yes and yes. =)

You can not get mail until the account is upgraded. But it will be in your mail box and ready once you get cleared.

And no linking them as nothing to do with it. If you upgraded all you have to do is wait for the payment process to be competed mine was done in 24 hours. And again done on a saturday unlocked on sunday.