TLC Prisoner of Azkaban Sweepstakes - over!

Hey guys - we hope you got your entry to the sweepstakes in before now, because the contest is over. Over the next few weeks we'll be sorting through the thousands upon thousands of entiries, and will notify you personally if you've won. Once we've formatted the entries to send to JKR, we'll update you again. (We're going to have to send her a book full of them - perhaps one the size of OotP. There, hah! Back at you, Jo.)
The answer to the riddle, as so many of you sleuths correctly surmised, was "time."