Well I was induced with my first daughter, and I didn't think the contractions were
too bad. From the time they put the needle in my arm to the time my daughter was born, it was 28 hours. I got my epidural around the 26 hour mark. So basically I had contractions for 26 hours without needing pain relief.
But obviously that will depend on your labor, your pain tolerance, and other factors. My next labor might be awful! I really don't know.