They say 6-7 hours but I think they probably go longer than that, most of the Yankee stuff seems to exceed the expectations!
I have nearly finished my Starfruit and Orange one, it's lasted about a month for a large jar, started to tunnel though so I used an illumalid on it and it repaired it's self! I was very pleased as I love this one lots! the only trouble with finishing them off so quick is that I have to decided on a new one now!