Early blight spores need wet leaves or humidity above 90% to germinate in temperatures above 47 degrees so temperature really doesn't matter that much, but optimum temps are above 80 degrees. Trying to time the application of Copper is not an easy thing to do and requires spraying the plants before conditions are right for the fungi spores to germinate. Can't say I've ever been able to time the spraying before an outbreak, but I can usually stop the spread using copper (frac code M1) or chlorothalonil (frac code M5) and sometimes mix them together. I may follow up if need be with mancozeb (frac code M3) but not often. Chlorothalonil is better than copper which is just fair, but these three are about the only ones you'll find in a store under various brand names used on tomatoes.

The names list above are the active ingredients and are found in most brand name fungicides. Mancozeb is harder to find, but Chlorothalonil is common in many brands.

There are many more fungicides but are for commercial applications and most require a license to buy and are from different Frac groups with strict precautions, so home owners shouldn't be spraying it around.

there is another Fungicide available to home gardeners with the active ingredient teboconazole (frac group 3) which is approved for almost everything except tomatoes, peppers and potatoes but I don't use it.