I really dont think there is a link either. I'm pretty sure my mum was in labour with all 4 kids almost a whole day each. My Sister was in labour with her #1 for quite a while (don't know the exact time) and ended up having an emergency c-section... normal C-sec with her #2.
I, however, didn't go into labour naturally, I had to be induced 2 weeks after due date and had DS in 3 hours. Labour started at 7:30pm and Ben entered the world at 10:47pm.

I was so scared I would have the same experience as my sister because we are so much alike (same height, weight, body shape etc... we even look alike!).

DanniiM - I would actually say that the time length of my labour was perfect (for me anyway)! It was over so fast. I didn't get the chance to use any pain relief, but afterwards i was so proud of myself and felt as though i could really work with my body properly.