Copied from http://www.urban-rivals.com/en/help/?category=0 (Game Modes -> Survivor)
In the middle of a series, you must suspend play for a maximum of 30 minutes in a row. After 30 minutes, you'll automatically receive your Jackpot and will be reset to a new Survivor. "Playing" means finishing your battles, not just staying in the room.
This basically means you have 30 minutes to play between matches before your score gets reset to 0