Oxytocin is a potent stimulator of contractions, which help to dilate the cervix, move the baby down and out of her body, give birth to her placenta, and limit bleeding at the site of the placenta. During labor and birth, the pressure of the baby against the cervix and then against tissues in the pelvic floor stimulates oxytocin and contractions. So does a suckling newborn.
See, I let down three days after my first birth which was a c-section after a LONG labor that went no where. But, I only dialated to 2cm after 42 hours.
The second and third were scheduled and it took 7 days for both.
I think the key might be in the cervix, as you suggested by the Oxytocin forcing dialation.