I'm going to go with a different viewpoint. If the project has to be done by mid-January, your trip is over Christmas, and you know about the assignment now, I would start the experiment as soon as possible rather than waiting to do it during your trip. My boys have done many science fair projects. Some worked out well, some did not. Sometimes experiments sound good on paper, but then they end up needing a lot of tweaking and retooling as you start executing them. You might find that you aren't able to gather enough data with your original plan and you need to rework it, a lot. Sometimes you think of supplies or equipment that you didn't plan on needing and make several runs to the store.
I would recommend coming up with the idea now and starting the experiment at home. One of my DS's favorites was watering plants with water, milk and soda. Only one plant survived. He had to figure out what may have happened to the other plants (too much sugar, calcium, etc.). It was an interesting project that took 3 weeks to complete. Then he wrote the paper, made the display board, and had some nice, moldy plants to for his display.
It might sound fun to do a science project at WDW, but it would also be fun to get a lot of the work done ahead of time and enjoy the trip homework-free.