When I was quoted I was told 15-18 months, then told 5-7 upon pickup. Is Invisalign cost associated with length of treatment?

My dentist told me that he does a tray a week with the movement at 1/8 mm per tray instead of 1/4 every 2 weeks as to not have so much pressure on the teeth. I called to ask about payment because obviously this is a huge difference in length. When they got back to me, he told me that the length of time/trays has nothing to do with the fee. He also told me that instead of changing the trays every week i need to keep them in for two weeks. Any feedback in appreciated.

No doctor answers yet