Today, CM Skerio answered this question on the Auditorium. According to him, characters are teleported to the reward room 10 minutes after pulling the lever. This way, teammates can no longer block the passage to the reward room indefinitely. This could either be done intentionally or unintentionally (in case of losing internet connection, for example) by those staying before the door that leads to the reward room.
Source: Post #39217872