What is the minimum sample size for this setting?

I have several mazes. They have one entry point and one exit. Some are ridicilously easy, some are really hard, some do not have a solution.

My goal is to find out if it is more convenient to solve a maze by starting from its exit.

The problem is i can only solve a single maze from its entry or its exit. I have no way of solving the same maze by starting from both the entry and the exit.

What should be the minimum number of mazes solved by each method, so i can say with a statistical significance of p<0.05 that it is or it is not easier to solve a maze by starting from its exit?