Tania,
Ignoring for a moment Mischka's mysterious Daconil ways,
, a copper containing product could help with prevention of Early Blight ( A.solani), which can occur both early and late in the season, but it isn't going to help prevent Late BLight (P. infestans), and Copper containing preps simply aren't as good as Daconil.
And please remember that even Daconil isn't as good as some products such as Tatoo that commercial folks have to help prevent Late Blight, but it's the best of what we have for home growers. And it IS the best for Early Blight (A. solani) when used on a regular basis.