My doctor said it was going to take nine months. After the first two months, I had to redo the mouth mold and send it off to Invisalign because my teeth weren't moving. Invisalign had screwed up on the first set so they had to reconfigure and I had to start over. So that added on another two months and my total treatment was almost one year and six months in the end.
I wasn't completely satisfied when the treatment was over and my doctor offered to put on regular braces but only the silver ones. So basically after I just paid $5,300 out of pocket ($6,800 less the $1,500 from my insurance), I had to start treatment all over again with silver braces.
I am 37 years old and the reason why I got invisalign was because I didn't want metal in my mouth. My advice is get the clear braces and don't waste your money on Invisalign.