Okay. Thanks for the help. The reason I asked is because I noticed some online races were timed races instead of laps. Just wondering how they did that and if you could do it in a custom championship.
AFAIK it's mainly a problem with the AI. They are not good at projecting their fuel load and such for a timed race, and there also may be issues recognizing if they are on the final lap etc. I hope that with the current advancements with the AI timed races offline will be available some day
For now I just set a lap time and then approximate the laps needed for a race of a certain length. Takes more time, but mostly works out OK.