It would be best to wait untill you don't have a time frame like that. But says, I think it was orangeman said, you prob won't get high the first time. Unless you smoke cigs, it will prob take some practice before you start inhaling correctly. If you were to get high the first time, it would last for about 1-2 hours if it is KB (good stuff) or about an hour if it is decent mids. But you may feel burnt out a few hours after you come down, which if you have to go home, you may look very out of it still.