I imagine it's pretty much a weekday operation, and I've noticed they seem to be done early in the afternoon (but I've only been there a couple times). The former air base is pretty much wide open and you can drive all over the place. The enginehouse is along the UP mainline, several blocks from the entrance. Suggest you act responsibly to avoid attracting the attention of any security they may have; it's an industrial park with trucks, forklifts, and rail movements, so drive carefully and mind your surroundings.