You're right, you are already screwed, stopping one day before injections won't have any effect.
You are, no doubt, a big girl and have made the choice to smoke. The best thing that you can do for yourself (and reap from this question on Real Self) is to commit to quit smoking forever. In the long term you will be helping not only your skin and wrinkles, but how about those lungs of yours?
On the positive side of things, smoking should not effect your upcoming Juvederm injections with you NP. Nor will drinking bottled water, or any of the other "old wife's" tales about those "smoker's lines". Your mitochondria will appreciate the extra oxygen they will be able to work with to help your skin once you quit smoking for good.
Good luck and be well.