As it stands, the collective Potato Sack-playing efforts of everyone participating will unlock the game at approximately 4:30AM EST on Tuesday. However, there might be a curveball. The "Auxiliary Power" counter, which adds up new "potato" achievements found in each game, is now counting down rapidly, toward ... something! If it's a timer, it will elapse around 10PM EST this evening. Meanwhile, some fans are taking matters, and potatoes, into their own hands, organizing the mailing of actual potatoes to Valve HQ.
Most of the games in the Potato Sack have hit their maximum playtime for the event, so if you want to help out by playing games, first check the GLaDOS@Home page to make sure you're playing for a purpose.