I think a good guideline would be to take some kind of action if the players fail to finish a game each half hour. Don't wait for disaster to happen. Don't just tell them at 3 hours the match is done.
I wouldn't be that TD under any circumstances or any amount of money because the players sloth would be made his problem.
Time limit is one rule, it's clear, no debating it.
The one that's behind can make a come back play and win or he can lose.
Its not gambling, its tournament play.