After a single dose of propranolol, it can last for several hours when used for performance anxiety. The recommended dose is 20mg to 40mg taken one hour before your performance. Larger doses tend to last longer. Given its half-life ranges from only 1.5 to 3 hours, the effects of propranolol dissipate fully by 24 hours (Shand, 1976).
Pharmacokinetics of propranolol: a review. Shand DG. Postgrad Med J. 1976;52 Suppl 4:22-25.