Officially? 24 hours. But honestly, I was never charged for a cancellation. I never cancelled unless I had gotten suddenly ill or there was an emergency (and I always communicated directly with them as soon as that kind of thing happened), so he didn't charge me. Same with my psychiatrist. I'm sure they would have if I abused the policy by cancelling a lot, but that wasn't the case. They were reasonable people and realized that emergencies happen.