According to http://www.ign.com/wikis/gcn-cheats/Cars_Cheats , IMSPEED is nonexistent on GameCube.

But, the VROOOOM code is said to give a fast start on GameCube, which is what IMSPEED does on PlayStation 2. CONC3PT supposedly gives infinite boost, which is what VROOOOM does on PlayStation 2.

I would assume that VROOOOM would be the official substitution for IMSPEED on the GameCube for the Any% Cheats category, but I would ask the moderators first to make sure.

RTA runs end when crossing the finish line on the last race, right?

From my understanding, full-game runs use RTA and include loading screens, while track-specific level leaderboard runs use in-game time. Is this correct?

Also, when does timing start and end?

Thanks :)