Dude, you've got *24 HOURS* of practice...<grin>.
Don't sweat it. For endurance races it doesn't matter where you qualify, and it doesn't matter where you are after the first, third, fifth, or one-hundredth lap. What matters is making sure you have your feces together to make it to the end of the race.
When I did the Longest Day in the early 90's I flew there never having seen the track. When I jumped in the car the first time it took about a half-dozen laps to get up to speed. It's handy to use the practice and qualifying sessions to get the general layout of the track, but you'll have plenty of time to figure it out afterwards.