My first daughter was 14 days post dates 33 hours of posterior labour - brow presentation. Very very ouchy!
My son I went into labour on my due date (he and I are both Virgos I figure this is because we like to do things PROPERLY!!!!!!) His was a textbook 4 hour labour and birth
My next daughter was born 10 days post dates - very fast and furious - 1 1/2hours
My next daughter was born on her due date 6 hours - text book gorgeous labour!

They are all different though there does seem to be familial tendencies for some women. I hope that your labour is beautiful whenever it happens...