Different species have different free-running periods also.
If you work with crickets , the first thing you would want to establish is if they have a circadian free-running period, and if so, its length. This is exactly what researchers do in order to learn more about the Clock. You can do things to the cricket itself or you can make alterations in the environment. To the cricket you might think about how the light stimulus gets into the animal and try to block that. You might give certain chemicals to the cricket such as caffeine and see if they have an effect.