1) The tooth involved. Most of the time multi-rooted tooth like the molars would normally take a longer time to treat than single rooted tooth like the incisor.
2) The dexterity of the professional. It is expected that a specialist in root canal treatment will be faster and take lesser time.
3) The duration of the pathology. Acute cases takes longer time because of the sensitivity and the excruciating pain that acute cases cause.
4) The psychological preparation of patients plays some roles in the duration for root canal treatment.
Root canals can be different lengths of time depending on which tooth it is, the reason you need the root canal, and whether you are seeing a specialist or not. That being said, most root canals are around an hour. Sometimes you have to go back for a second visit which is around 30 minutes. Good Luck!
Dr. Alexander Ferdkoff