Extensive research over long periods of time shows us that average float time of the balloons filled with Balloon Time helium, is 13.2 hours,. However, we conservatively state on our package that balloons will float for 5-7 hours. Float time can vary significantly based on the level of inflation (underinflation, regular inflation or overinflation), size of balloon (9", 11" 18") and external factors such as temperature and humidity. (Balloons float longer in colder temperatures and in higher humidity.) Balloon Time recommends inflating balloons 1-2 hours prior to the event for the best results.