As others have said you cannot predict how long it will take but the most important thing once you have an instructor you get on with is continuity, continuity and continuity.
Regular lessons without overloading yourself (with regards to the rest of your life) are vital. One/two lessons a day would be ideal if you can get the study and preparation done between them, two, three lessons a week would be fine, one a week would be OK but stretching it out rather imho, and less than that getting counterproductive. Continuity minimises the three steps forward, one back situation which costs £££.
Arrange your life for a month or two, make a plan and book up at regular intervals and get on with it.