Ive been looking at the numbers for radiation, UVA & UVB since its seems to be the one which a greater amount reaches the surface.
A. From what I was able to gather, at noon we get a max of about 11uW/cm2 which i believe translates to 0.1W/m2.
B. Studies i found online stated between 1-250 J/m2 required to inactivate them over a range of microbes including virus.
C. I believe that means that 0.1W/m2 we get at noon, over 10 s = 1J/m2, which would be the lowest threshold and 2500s would result in the upper threshold of 250J/m2.
So 41 minutes at noon is a nominal approximation for the time required on a sunny day (say at latitude 15 degrees)?