My hands, neck shake; face twitches and voice trembles whenever I am in a stressful situation. I have been having this issue for years and I thought this would go away after enough stressful encounters but I have had no luck with it.

 I have a very important interview coming up and have decided to take propranolol 40mg before the interview to stop the shaking. 

I wanted to know how long before the interview should I take it and for how long the effects last?