I just had recently a rootcanal retreatment for a molar, and it was done by a pretty young female dentist who was extremely careful, and maybe even a bit unsure, so it really took some time!
On the first visit she drilled more than one hour, and after that I needed to go to a 3D x-ray to an separate office, which took about 1 hour. After that I returned to chair for almost 2.5 hours! And in that point both she and me were pretty tired, and she proposed to continue next day. So the next day she continued 3.5 hours more, and then the root canals were finally clean and filled with a medication!
The final filling took about 1.5 hours, and a new crown would still be needed fot the tooth. Although, I have now again after 3-4 months some feeling in the tooth, so in the worst case (or actually the best case) the whole retreatment has to be done again! Or the tooth needs to be extracted.
I have also earlier had multiple long visits like 1.5 - 2.5 hours, due to root canals, root canal retreatments, crowns, braces etc. My teeth are really much treated, so I have gone through a huge mount of different treatments, just name it!