You can only use an MX-5/Miata/Mazda Roadster on the Tsukuba 4h endurance. Also I don't know how many laps they do, but some people do use the X2010, race for a few hours, leave it unpaused for the rest of the time then complete one last lap after the 4th hour. It'll be easy enough to work out when you're doing it, though, just make a note of their lap times on the first lap (almost always the slowest lap), work out how many laps they could do (exclude the extra time pitstops take just to give yourself a bigger margin), do more than that number and get close to the finish line, set a timer on your phone for however much is left on the clock, go away, come back when the timer goes off, cross the finish.