We usually cancel by 4:00 after studying the radar and reports from various weather stations. If it's been pouring all day and flooding we may cancel earlier. We have had rain dates in the past, sometimes on our main calendar we'd have a TBA notice on those dates. Sometimes we had the need to use them. It is a tough call, having an outdoor haunt can be frustrating but in the nice weather it's awesome.
Good luck....stop by sometime.