You can take it as you please, just check if your body have contraindication. Normal dose is up to 240mg per day; I think I'm gonna take 200mg an hour before SN so I don't puke it all.
Propranolol appears in the blood after 30 minutes and has a maximum effect between 60 and 90 minutes (other source says 1-4 hours) when taken by mouth. Common side effects include nausea, abdominal pain, and constipation. It should not be used in those with an already slow heart rate and most of those with heart failure.