Propranolol typically starts to reduce the physical symptoms of anxiety within about 1 to 2 hours after a dose, with peak effects often occurring within 1–4 hours for immediate-release formulations. The duration of action for a single dose generally ranges from around 6 to 12 hours for immediate-release forms, and up to about 24 hours for extended-release. The exact onset and duration can vary based on the formulation (immediate-release vs extended-release), the dose, how it’s taken (with food can alter absorption for some people), and individual factors such as age, other medications, and liver function. If taken for performance anxiety, many people find it helpful when taken 30–60 minutes to a couple of hours before the stressful event to allow time for onset. Important caveats:

• Propranolol does not treat the underlying anxiety or its triggers; it mainly mitigates physical symptoms like rapid heart rate, tremor, and sweating.
• It should be used under a clinician’s guidance, especially for long-term use, and is often part of a broader plan that includes therapy or lifestyle strategies.
• For some individuals, onset can be shorter or longer than the typical window, and side effects or interactions with other medications can affect timing and suitability.

If you’d like, share your specific context (formulation prescribed, dose, and the activity you’re preparing for), and I can tailor the timing guidance more precisely.