I'm not so sure. At the very least Freitag would have to be dative because we now have 3 nouns without prepositions, wir is nominative and Wein is accusative and freitag is clearly not Genitive so it must be dative.
It is because in plain sentences, a verb has to occupy the second place from the beginning:
- “Wir trinken Wein.” 1st place: who, 2nd place: verb, 3rd place: the rest
- “An jedem Freitag trinken wir Wein.” 1st place: when, 2nd place: verb, 3rd+ place: the rest.