I was told my Invisalign would take 12-15 months however it's been 17months and I'm only half way.
I was initially only concerned about one of my teeth which did not fit in due to overcrowding but was convinced to buy Invisalign for both top and bottom teeth. At the moment I currently have a row of brackets on four teeth, Invisalign for top and bottom, buttons on numerous teeth and am required to wear 2 rubber bands on my teeth. One rubber band goes from the top tooth to the bottom, making it very difficult when speaking as I can't open my mouth very wide.
Orthodonists aren't concerned about personal comfort they only care that teeth are exactly straight and perfect. Some of my Invisalign also don't fit properly due to my braces and yet I am still required to wear them, but because they don't fit properly it makes me talk differently and people often can't understand what I'm saying.
My Invisalign treatment was very poorly managed. If possible you should get your Invisalgn made in batches (not all at once), because if something goes wrong then all your other Invisalign won't fit. It is supposed to be quicker than braces but my treatment will last at least 2 years and possibly much longer. I am currently thinking if I should even bother. I originally went for Invisalign because I didn't want it to be obvious but it is sometimes very obvious. In my current Invisalign the top sticks out and looks ridiculous because it doesn't fit properly.
Ironically the brackets that they fit on my teeth has shifted the tooth that I was most worried about in the first place. I probably could have gotten away with something like that and skipped the Invisalign alltogether but they never told me about that.