No no no. Please no time trials. There are already nearly perfect time trial videos out there that were done on the consoles themselves. (Edit: Well, that's actually a lie, since some of the best videos aren't really available)I say the only way to make an interesting run would be making GP runs, with plenty of luck and glitch abusing. I'm not sure about the format, ie one video per cup or what. Also, 150cc mode and special cup must be unlocked, so that creates even more problems. (there might be a keypress combo to unlock everything at the start, but I don't know).
If you insist on making time trials, here are the times that must be beaten for it to be worth anything (assuming the NTSC version will be used):
http://www.geocities.com/TimesSquare/Dome/3346/ntsc.htm
This is the site I found (geoshitties sucking isn't my fault):
http://www.geocities.com/smkplayerssite/
Here are some videos:
http://www.geocities.com/smkplayerssite/smk_proof.htm
Whatever the type of run that is made, someone needs to find out how the hell those top times were achieved.