My t has a 24 hour cancellation notice; however, she will make exceptions if you have a legitimate reason for cancelling and weather is one of them. She has called me to tell me she couldn't make it due to ice in her area. She also canceled when we had a tornado warning. I've canceled last minute bc my car wouldn't start (she didn't charge me). I"d definitely ask, but I'd think as long as it's reasonable, they wouldn't charge.