How long should a mother wait after smoking a cigarette before nursing her baby again?

Upside of smoking? Your wish to protect your baby from the effects of smoking is admirable. Where is your wish to protect yourself?
Don't smoke. BF is a great process, but you are reducing its benefits if you smoke. The nicotine will cross into the milk & baby.You make milk continuously, so there is no happy hour delay that will clear it. You carry smoke to baby on your clothing and hair. Babies are at greater risk of crib death and respiratory illness if you continue.
Forever! I am so happy to see you are nursing! But the answer to your question is "Forever" You do not want these cancer causing toxins getting into your baby's system, I have to believe! You simply must drastically wean your cigarrettes now and quit. You CAN do it! Consider a medication like Wellbutrin (bupropion) or Chantix to help you quit. The side effects of these are miniscule compared 2 cigarette toxins.