Just a joke for those learning English, sometimes you'll hear, "I only drink wine on days that end in Y." Other times you'll hear, "I only ___ on days that end in Y."
techincally we don't say it like that in English...it doesn't sound natural
You may have figured this out, and I am still pretty much a beginner, but the quartas means fourth, and I think feiras refers to each day of the week in this case. Therefore, the fourth day of the week (starting Sunday) is Wednesday.