Should these (e.g. Quercetin) be taken before symptoms or after symptoms appear?
Before, Quercetin is zinc ionophore
Prophylaxis
While there is extremely limited data, the following cocktail may have a role in the prevention/mitigation of COVID-19 disease. This cocktail is cheap, safe, and widely available.
Vitamin C 500 mg BID and Quercetin 250-500 mg BID
Zinc 75-100 mg/day (acetate, gluconate or picolinate). Zinc lozenges are preferred. After 1
month, reduce the dose to 30-50 mg/day.
Melatonin (slow release): Begin with 0.3mg and increase as tolerated to 2 mg at night [13-16]
Vitamin D3 1000-4000 u/day
Optional: Famotidine 20-40mg/day
His Update #59 is worth watching. You will get the dosage regimen the doctor recommends.
Coronavirus Pandemic Update 59: Dr. Seheult's Daily Regimen (Vitamin D, C, Zinc, Quercetin, NAC)
Unfortunately, the morons at YouTube took down several of his scientific lectures because he was assessing HCZ.