Youhave to take it at least one hour before stage so it's effects are at maximum.
The effects will last for hours. After a few hours after the shot, it will flatten you out if you don't eat enough - eat your normal comp day food. If you do eat properly, you won't flatten out and it will work straight into the night show.
DO NOT use it again in evening, as you most likely will pass out - it has a build up effect. If you use 10ml in the morn and 5 ml in the evening, it's no different than using 15 ml at once.