i am about to go through a similar thing... i am having knee surgery on 7/29 and i have a four month old little girl that is exclusively breastfed as well. i am planning to have a 24-48 hour stash minimum ready. i am guessing approximately 24 hours, but it will depend on the exact mix of anesth i get, fortunately for me, my husband is a pharmacist and will ask the anesth dr what he used and what doses, and he can figure out based on my dosage and bmi how quickly it will leave my system. i also have a 3yo and a 6yo, so i know what you mean about pumping. i have been pumping every night right before i go to bed lately. it only takes me about 10 minutes. i'm hoping to get off the pain meds quickly so i can get back to nursing her asap. i don't mind nursing her on a small amount of pain medication, but i want to be 100% positive that the anesthesia is out of my system.