Well I can't speak for myself, but can speak for my mother.
I was her first: born two hours after the first contraction.
My brother came next, in about 4 hours.
My sister next - they didn't even get her into the delivery suite for that one - she was in the "getting ready" room taking off her pantyhose and oop...out came the head!
My other brother was born gosh, well about 4 hours again I think was the labor.
The one exception I do believe was brother who died, who was born fairly quickly, but more slowly than the others - he passed away from a placental abruption (the same as my Josie) at the hospital before being born back in 1986.
All four live births were natural and totally un-medicated with anything. Finn, who died, was medicated with gas and air, I think - and a shot of narcotic because the emotional aspect made the labor very hard to handle, obviously.
So in her case certainly, it was always pretty quick. Because of her history, I am being treated as a woman who may well have a precipitous labor as well. We're built the same, my mother and I, so it wouldn't surprise me.
Hope that helps a bit!
Mama to Josie , lost 10/10/08 at 37.4 weeks .and my rainbow baby, Isobella Mai ...born 1/12/2010
!Pregnant with Prairie Baby, AKA #3. Due October 17th, 2015.