My DSs labor was 45 hours from first "Oh, that is a contraction! cool!" to vaccumn assisted delivery. However, I spent the first 34 or so hours at home. After about 16 hours it got too painful to sleep through, and I woke up for every contraction, but napped (not much sleep) between them. The past 11 hours or so where in the hospital, on my back, epidural, constant monitoring, IV, etc. When I got to 10cm the epi stopped working and I was told when to push, after 3 hours I was too tired and they used the vaccumn, which at that point I wanted.
So, I honestly think that had I been at home or in a birth center I probably would have had a 38 - 42 hour labor. Since after 34 hours I was only at 3cm, then an hour later 4 (got IV, water broken, epi, etc), then 1 cm an hour until I stalled around 8 - 9. Was agumented with Pitosin. However, I will never truely know how long my labor would have been, but at least 38 hours.