I did that race on the Peugeot 908 HDI totally stock on racing hards and racing mediums (mixing them between stints).
I did 185 laps taking it lightly, but nonstop. AI did 178 laps, 21h on dry 3 hours on wet.
AI laps at 8 min on dry, and like 15 min (yeah, 15!!) on wet.
Actual playtime well, 24h.