The risks of smoking before breast reduction are high, that is unless one doesn't mind a higher chance of the nipple turning black and dead and falling off. In addition, there are also risks of poor healing. Wounds that stay open for longer than expected have a higher risk of infection. Any of these types of complications may require additional surgery, harsh antibiotics, prolonged wound care, and a less than optimal cosmetic result.
The nicotine assessment test is designed to protect you from these complications, or at least reduce your risk of having them compared to an active smoker.
Trying to figure out how to smoke as long as possible while still achieving a negative test, is not a productive way to look at the situation. What you really need to know is how soon you need to quit before the negative effects of nicotine will no longer be there to affect your blood supply and wound healing. No one can definitively tell you that because the test only assesses nicotine metabolites, not your personal physiology.
Most board-certified plastic surgeons will recommend that you quit smoking for at least 4 weeks prior to surgery in order to decrease your risk of complications. Of course, we want you to quit indefinitely to protect your health and beauty!