I didn't know καιρός could mean "weather." I normally associate it with time, especially opportune time, as it is used in koine Gk (Mark 1:15). But even in ancient Gk it could refer to a season, so the modern Gk sense of weather makes sense. When I first came across this modern Gk word καλοκαίρι I thought it was great that the word for summer is "good time." I guess it refers to the opportune time/weather to plant crops.
Thought you would both be interested in the etymology of καλοκαίρι:
From Byzantine Greek καλοκαίριν (kalokaírin, “good season, good weather”), from Ancient Greek καλοκαίριον (kalokaírion, “fine weather”).
Also, brilliant learning strategy Diana :)
No, it isn't, it must have been accepted as a typo. You used the wrong ee vowel at the end and Duo does not reject answers for misplaced accents either. Remember that neuter nouns ending in ee use an -ι in singular; if you see a neuter noun that ends in -η, that's a plural form.