I think that labour lasts as long as you need to learn all the lessons required for this particular child. Many cultures also believe that the baby’s personality determines with the progress of labour.
One of the family doctors I know said that all three of her boys had labours to fit their personalities. One came flying so fast that his cord broke. And that’s how he goes through life - flying headlong into things, both physically and emotionally. Another son takes his time, considers all his options, then considers them some more. As a result, his labour took a long, long time.
My daughter is strong, powerful, never wanting to follow the crowd. When I was in labour, her head was trying to forge a new, totally different path - out my hip. Later, her high school math teacher said that she would pound away at a problem for a long time, only to later discover that if she just turned the equation around, the simple answer was there, in plain sight. That sounded just like her labour. She eventually tilted her head, and came very quickly.
It’s interesting to note that my clients who have the quickest births often have the hardest time adjusting to parenthood. They often tell me that they just can’t figure out their baby. In a 15-minute labour, there’s not much time to learn the lessons that you need to parent this child.
So, be thankful if you have a slow, gradual labour. There are many benefits to the lessons learned during this time - lessons that you will draw upon for a lifetime. You might even begin to understand that labour and birth is something that’s out of your hands, and that's okay. When things are slow, it's not "your fault." It might just be your baby speaking to you through your body...