ive heard that death can take anywhere from 7 minutes to 1 hour lol. I guess not many people would know because most people that are found alive are found in 5 mins or less. and others that succeed alot of the times arent found for hours or even days. also I think it has to do with positioning. If you choke to death then it takes less time to die but longer to pass out. carotid artery is the other way around in most cases.
Id say make sure you will be alone for at least 1-2 hours just to be super safe if you are considering this method