'All bets are off ' does come from the world of horse racing, usually when a race was cancelled due to a severe change in the weather, for example. The race would be rescheduled and betting would start again. It has come to mean' anything can happen' because the situation has changed so much that anything agreed to before can no longer be honoured. It is usually used negatively, like the phrase' the gloves are off' which means we are no longer friends, anything goes, and it won't be pleasant! Examples of it in use: 'If it can be proved that a country has attacked us with biological weapons, then all bets are off!' When a judge doesn't send a criminal to prison for his crime, he might say to him' If I see you in my court again, next time'all bets are off' and you will go to prison!' 'Timekeeping' is usually being punctual. A person is either good at timekeeping, or not. ????

I'd say it occures when a bookmaker isn't certain about situation and all factors have become unpredictable so bets are off. Anything can happen. Rules have become obsolete in an instance.