What can I do for conflicting Invisalign recommendations?

With moving teeth, we can only guess how long it would take. Our experience is what makes our guesses more accurate.
One thing to ask yourself is are you choosing on price or on length of time? Every office has their own fees, so there WILL be variations. Your first doctor simply adds the Invisalign lab fee on to his wire ortho fee.
Until impressions are taken and Invisalign computerizes everything, it's all a guess. Even WITH the 3-D images, we don't know that your teeth will move as planned, so the length time is never 100% predictable.

It is hard to imagine the case being too severe. Invisalign does have its limitations but the limitations can be overcome.

If it were me, I would go to an Orthodontist that has the most experience. I would rather go to a heart surgeon who does 200 a year rather than one who does 1 per year. Sometimes the more experienced charges less since he is more efficient.

 

Unless you have had impressions of your teeth taken and submitted to Invisalign, the dentist is just giving you his best guess (from his experience) in how long it'll take to do the full course of Invisalign. Invisalign will not determine the number of trays needed until they actually go through the scanning of the impressions and begin the fabrication process for the trays. I honestly do the same thing. My disclaimer to patients is that I AM making my best educated guess about how long it'll take with Invisalign (+ or - a month or two). Hope this helps.