hello and welcome to hcm forum,
i would be glad to answer your query,
first of all i , with all due respect to you and your dentist i would like to inform you that being a dentist we cannot assure you of the time period a tooth takes to moves from its original position to a new position.
you have not mentioned your age here, but i believe you might be older than 20.
ideally, orthodontic treatment is done during the growth years (puberty),
but in some cases, we do perform orthodontic treatment beyond that age as well, as in your case orthodontic treatment can be done but the time & the results cannot be decided before.
As the teeth and jaws have developed fully, therefore to retain them in a new position , you will need permanent retainers which hold the teeth in an appropriate place, do not worry these are not visible to anyone.
i would advise you to get the orthodontic treatment done but avoid unrealistic expectations,
just have faith in your dentist.
i wish you good health,
take care.

Hello there...i can/ any one can comment upon the time only if one can examine you clinically... orthodontic treatment has various factors that would influence the outcome....severity of your problem, condition of your teeth, gums, the amount of care you take during the treatment, regular periodic check ups and finally the skill of the doctor...At times the teeth does not move as how we want it to... that is when the treatment delays...certain amount of pressure is required for the movement of the teeth more than that would lead to mobility of your teeth... As you say your doctor is experienced he must have judged your condition before telling you...must be he is confident of finishing the treatment.... Go ahead....all the best