A quote from a former manager at YC - - - - - >
Most tarts will provide fragrance for between 8 and 12 hours. This means you can usually burn two tealights for every one tart. Unlike oil, the liquid in the tart burner will not evaporate. Instead, you will know that the tart is "spent" after you can no longer smell its fragrance. Whenever you are finished with your tart, the easiest way to get it out of the burner is to let the hot wax cool and harden. Then, place your tart burner upside down in your freezer for 15 or 20 minutes. The wax will shrink and pull away from the sides of the dish, and after being in your freezer for awhile it should become loose enough to just slide out or be gently pushed out with your thumb.