The regulation in force states that a bet on a sporting event is considered valid if the event takes place within 12 hours following the date established in the official programme.
After this deadline, you are entitled to a refund of your stake if you have placed a single bet. If, on the other hand, a multiple bet has been placed, the postponed event will be paid out at the original odds and the remaining events are paid if successful.
There are exceptions to cancelled/ postponed matches when it's a tournament (aka tennis for example), if Player A vs Player B is postponed to 1 day later, and in that 1 day Player A & Player B do not play any other matches, then it stands.
Our article What happens if an event is suspended? can be viewed for more related information.