If you have an electric wax melt burner, you can usually leave it on for up to 10 hours at a time, although this will likely mean your melts are used up quite quickly. The manufacturer should provide guidance on the maximum amount of time you can leave the warmer, so always check the packaging. Candle-lit warmers offer a shorter burn time, ranging anywhere between 4-8 hours. If you use a 4-hour tealight candle, then this will help the melts to last for longer.