Uh... You can set the race laps to whatever you want to via the track.ini file. If you wanted, you could make Watkins Glen 1,000 laps. I am sure after that, you wouldn't have arms though.
I tend to run half the distance of a real race (two hours). If you play with the .ini, you can get some exciting racing.
To find the .ini, go into your Papyrus Folder > Tracks then pick a track and look for the track.ini folder. Open it up in Notepad or whatever, and edit it as you would like. You may want to save a backup in case you mess something up though. Hope this helps!
I usually race 30% races for my main offline series and 25% for the lower division series. Most of them last just under an hour or right on the dot even with a caution or two in it.
Erm usually 15-20 % - it's hard to get through them if you race the way I race - under two hours at a road course. Good thing they have runoff room. I'm even a road course specialist but the A.I. gets annoying. Time for some .ini edits lol.
OP: If my wife is asleep, I crank up the laps for about two hours worth. But usually just work out whatever works out to 20, or 30 minutes. I race the week by the Nascar schedule, so it depends a little on where they are too.
I'm editing the .ini too.
But it's pity, that there is not any way how to save race and then load it later. In the times of DOS there were a utility, called GameWizard, which allowed player to save the content of the memory do disk, and then back to memory. But game at that time were small and this was also not reliable... (and the games didn't need lot of drivers for video-card, driving wheel, sound card, etc)...
If I do an offline season, I double-check that the default event laps value is correct in the track.ini, and do 35%. Like Mystical mentioned, it usually works out to an hour or a little more. If I wasn't married, I'd definitely do 100%...I like making races as real as possible...just can't find that amount of time in one chunk anymore...haha.
The 512 thing in interesting...maybe because 500 is the max real-life laps NASCAR runs in a race, and 512 is the closest even 2^n (1,2, 4, 8, 16, 32, 64, 128, 256, 512) number...which is a nice even 1000000000 in binary...good place to stop if you're a computer programmer with no forseeable need to go further.
I run 25%. I think it's the perfect amount for me. You have to pit once or twice, and the race isn't too long. I typically don't have time to drive a full 100% race. Back when I was a young sprout, I did do some full length races on the old EA Thunder games. As for NR2003, I used to be terrible at getting on/off pit road. Then I raised it up to 25%, and I've improved quite a bit.