Zoono, page-7

If you understand the technology you have the answer to how long ZNO products are effective i.e until they are removed by friction or skin exfoliation.
London Underground did their own testing & I believe they are applying every 21 days & that would be a very high friction environment.
LU & other UK customers are going to support ZNO with their case with UK standards, the testing carried out for COVID-19 was carried out by an accredited UK laboratory.
So have I no doubt they will get clearance to make a claim in the UK, to what level I could not speculate.

I don't believe there is a standard test for 30 days efficacy against viruses hence the reason why ZNO never made the claim about COVID-19.
Basically they are going to have to test or present evidence to support any claim they want to make before making it,not unreasonable.