If you keep all of the N down, without throwing any up, I think a couple hours would be a safe bet. You know, just to be safe. If you throw up the N rather quickly after consuming it, and not much has had time to absorb into your system, this can pose a problem. You may become unconscious, but do not die. if, however, you have another glass of N ready to consume should you throw up, you can immediately consume the second glass and, hopefully, get enough into you to ctb. if you want to be safe, I'd say 2 to 4 hours. Most likely you will have ctb sooner, but I'd rather be safe. If the N doesn't work (because you threw it up) and you only end up unconscious and then get found, you have other problems.