|MadSci Network: Chemistry|
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.
How will you measure rate of burn?
How long will the freezer candle stay cold?
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).
Try the links in the MadSci Library for more information on Chemistry.