Everyone s different but with my eldest who was back to back, labour lasted 3 days but it wasn't too painful so I didnt even realise it was labour as I expected it to be much more painful I thought it was braxton-hicks. The active labour lasted (and the length of time i realised i was in labour) about an hour and whilst it was painful I didnt need pain relief. So from my experience back to back labour wasnt longer or extremely painful. For me the fear of the pain during labour was worse than the reality, I had heard so many horror stories!