As an R1 candidate from last year, I can say this is an extremely tortuous period that lasts over several weeks. Most of the invites last year came out in the first day and the remaining 100 - 150 trickled over several weeks. If you want to retain your sanity, I would recommend just waiting for the e-mail. Checking multiple forums will consume your life. On the other end, if you get the e-mail, sign up for the interview immediately - the slots are take over in the matter of minutes/hours.