Thanks for the info, I always thought it was server side.

No, wasn't I the one who thought it was server side? You were the one who said it's much more likely to be local.
But yeah, I also got suspicious that it was local a while back, using a USB Gecko. When using the "Attack of the Dodos", I used a USB Gecko to pause the game when there was nobody connected in the race anymore. The Wii did not disconnect despite being paused, and only disconnected once it had been both unpaused and reached the 5:56 limit. However, Wiimm's clarification is excellent, so thank you for the information!

I hope you don't plan on doing a 10 Minute timer limit because I really dont want to play on 10 Minute tracks.

We only tried this out to see, if the server sends a "race end"-packet after 5:53, then we might have had the possibility to kick somebody (cheaters) from our server without being "rude" and closing their connection.

Even if you close their connection the Wii wouldnt explode but simply say that your connection was lost.

The information packet is only sent each 30 seconds. So if we want to kick a cheater by closing his connection, he stays in race and can cheat for 30 more seconds...

But if we would modify the MKW main.dol/StaticR.rel to continuosly listen to the server, we could disconnect them any time.

That would be a big modification. The packet is sent from Wii to Nintendo, and if the Wii gets no answer, it goes offline. So simply closing the connection on server-side will allow the player to stay in the race for up to 30 seconds.