My question is: how far back(exact time) are drugs detected in a newborn baby, placenta, & umbical cord with diff types of testing (hair, poo etc)?

Drug screening: not every newborn would be screened for the drugs, only those who condition seems to be affected by it: clinically or inherited, or if there is a maternal history of abuse. urine test is fastest and shows the latest pregnancy drug use, meconium and hair show longer back use in pregnancy, but no exact timing could be given.

Varies with test/amt: Detection varies with the test, amount consumed and material tested.Urine clears quickest,blood later.If suspicious,I test meconium, the first poo,which begins to form about 12 weeks and remains until birth.Hair could be tested, but I've never herd if it in newborns. Timing is non-specific, since heavier users will leave more to be found.The meconium is good for at least several months back.