According to the PPH, 40 minutes at least.
I saw a person ctb by SN and about 10 minutes after drinking it, he was kinda unconscious. I say kinda "because" he was mumbling and it seemed he wanted to talk but at the same, it didin't look as if he was in pain. Then, about half an hour later, he stopped moving.
I think it's generally 40 minutes but just in case, I would drink SN on a day in which I knew I will be alone for at least 6-12 hours.