I still have my OG tubs and I take 1 scoop pretty much exactly when tiredness hits me and I need to stay up, which is usually around 2 am. This perks me up big time until about 6 am, at which point I will crash violently unless I ingest another scoop, which I usually do. This lasts till 10 am, and boom, all-nighter accomplished. So about 4 hours per scoop for me, and be prepared to get really tired when it wears off (perfect for bedtime).