Since I don't use them I'll leave how long to leave it on to the people who do use them, but I'd just like to toss in a warning. These things are known to thin your horse's mane out, especially when used over a long period of time. The horses I've known who wore them regularly always had beautiful coats and tidy manes, but thin! And really not that good-looking..I believe it has something to do with the lack of oxygen. Just something to think about.