If you have an existing account with pool and have previously aquired domains through them, payment would normally be processed on the same day and you will get an email from the acquiring registrar within a few hours with the account details.
If its your first acquisition from pool than it could take a few days, in this case I would recommend you check the whois to see who the registrar is and send an email to the registrar's support requesting for login info otherwise it could take a week or even more if you just wait.