Not sure if im much help but my bub had a serious constipation problem too,she never was when breastfed,im talking like 4 poos a day!Then i put her on s26 and she didnt go for 4 days!!She was soooo bad constipated crying etc was awful i did the brown sugar thing but it didnt work all that workd was daily giving prune juice which i wasnt comfy about,so i swopped to Novalac it was great!She was on it for a while like a month pood everyday but i thought id try again on a different formula as a few people said s26 was known for constiaption so i tried karikare but worried as didnt want it to come back but shes been fine since!!goes everyday no worries.i keep getting told to increase her water but she doesnt really like it,also shes strateds solids but still hasnt been constipated on karikare so for me that ones been the best,as far as how much time i dont know i think someone told me 2 weeks once but unsure.Hope that helps a bit!