My mum's labours:

Me (38w, spontaneous labour) - Around five hours.
Brother #1 (34w, spontaneous) - About an hour AFAIK. I'm pretty sure she said she went into labour at lunchtime, and he was born at 1:30.
Brother #2 (38w, spontaneous) - Three hours at most. He was born around midnight, and Mum wasn't in labour when we went to bed that night.

My labours:

Ianto (32w, induced) - About five hours from first contraction.
Amelia (38w, induced) - Eighteen hours from first contraction.