Rusty_Nails did you do the slider thing and actually enter the race? because the numbers on the slider don't change but when you start the race is says 1 lap. You can also see that it is a 1 lap race in the pit-stop strategy screen.
Exactly! Thanks Pady20000. To summarise again:
1) Go into the pre-race screen where you can choose the number of laps/race length.
2) Activate the cheat and move the slider (anywhere, it doesn't matter), and no, you won't see the values change but they are doing!
3) Start the race and turn off the code for safety (to prevent any possible side-effects, although there shouldn't be any).
4) Play a short race!
~PhoenixCH