10 days. Also, this idea partly came in a dream. While JK has always said that Dumbledore is, and forever will be, dead, she has never been able to give a definitive answer to whether Sirius is actually dead. Also, I read somewhere (Possibly even in this thread, I just can't remember), that one person will sacrifice his own life to bring back someone else. That's where I believe Wormtail will repay his debt; sacrificing his own life so that he may bring Sirius back.