I have an audition today i have been given Beta blockers?

Hi ok my daughter models and i went to the casting with her and they roped me in to it if i get the job its lots of money for me anyway! Its a video casting today i am so scared as with presentations in the past i shake and can not speak! I have been given 4 10 mgs Propranolol the audition is at 2.45 when do i take them to feel the affect thanks