The women are trying to raise money and awareness for Cystic Fybrosis. The rules are clear and finite: 20 women per team, they cannot leave the rink, one second late from break ends the record, injury time is tacked on to the end and injured players cannot be replaced, to name a few.
Per Puck Daddy:
There are no periods in the game; it's just one long competition between two teams of five skaters, one goalie and a substitute on the bench. Their "sessions" run four hours, followed by an eight- or four-hour break for nourishment, medical attention and sleep while another shift takes the ice
They are currently at just over 121 hours. They plan to be on the ice 243 hours, about an hour over the record. You can watch live stream of the game at http://longestgame4cf.com/.