Re: Is this a good science fair project for a 7th or 8th grader

I agree, your experiment is fine if you up the level of treatment in terms of how carefully you control/monitor the data and other aspects of the experiment.

For example:
How will you measure rate of burn?
How long will the freezer candle stay cold?
etc.

As for predicting the amount of time there might be? I cannot give you any useful information. BUT showing data that shows there is no appreciable difference is as useful/valid as having results that show a difference (like debunking a myth).

Good Luck.