Adding more sealant doesn't add to the the life of the original sealant. It just starts your 8 to 12 weeks over again. It's like a gas tank. You are only going to get so many miles out of a full tank of gas no matter how often you fill it before it goes empty. If you will get 6 weeks out of a coat of wax and you put a new layer on 5 weeks into it, then you just get another 6 weeks.
QD doesn't help extend the life of anything. It usually just adds shine and gets the dust off. The only thing that will aid in the life of a carnauba is keeping it out of the sun and out of the rain. That will squeeze every possible day out of the product. Or you can just wax your car once a month and forget about how long it lasts. I never just wax my car and wait for it to fall off before I wax it again. I usually wax it every 3 or 4 weeks so that it always looks fresh. Durability really means very little to me as long as it will look good for those 3 or 4 weeks between coats.