It depends on the strength of the SN, your weight (if you are heavy you will have more blood that has to mix with the SN for example), how much you take.
If conditions are ideal such as you have very pure SN and are a normal weight, under 15 minutes until unconsciousness.
I recall years ago, one man was saying he was 500 pounds and after saying he drank SN continued to chat normally in his posts here for over an hour. He never came back to post again after that.