I get this question a lot. And my first response is "I can't tell you that because every dog is different." Some dogs learn faster than others, other owners are overachievers in working on their homework during the week. What I can tell you is that after an initial consultation with you and your pup, I will tell you what I think you can expect from training.
The follow up question is usually, well what's the average amount of time. Again this is a case by case basis. I have multiple clients who only have to have 1 session with me and just keep me updated over the few following weeks. Other clients I work with on a weekly basis for months. It simply depends on your individual dog and what training you need and how far you want to go in your training.
Lastly on this note, please be vary wary of any trainer who will give you a set number of sessions to train something ahead of time. Dogs are individuals, and just as a good trainer won't guarantee results, a good trainer won't be able to give you an exact time frame on training.