How long can you leave a belly button piercing out before it closes?

It depends on how old the piercing is. If it's over a year old, then you can go a couple of days. If it's under a year old, then a couple of hours. The newer the piercing is, the less time you have with it removed before it starts becoming difficult to put it back in. If it closes, then go in to see your local professional body piercer for some help.