Heavy smoker for elective hernia repair, Smoking should be stopped before how much period

Cessation of smoking : 12hrs : reduces CO-Hb,hence increases oxygen carrying capacity 2days : CVS : aboloshes nicotine effect on sympathetic system stimulation, hence HR & BP normalises RS : Improves mucociliary function 2weeks : Sputum volume is reduced 2months : Relieves bronchospasm,decreases bronchial secretions,Chronic broncitis is reduced,Improves lung function,immune function returns to normal,hepatic enzymes returns to normal.