On Friday or on Fridays, which would be the better reply?

Do you have to go to lessons every day?

Not every day, but I have to go on Wednesday and Friday.

Not every day, but I have to go on Wednesdays and Fridays.

Question

On Friday or on Fridays, which would be the better reply?

Do you have to go to lessons every day?

Not every day, but I have to go on Wednesday and Friday.

Not every day, but I have to go on Wednesdays and Fridays.

Answer

If you're describing your regular routine, it's the second one. You go to lessons twice a week, every Wednesday and Friday.

If you're only talking about this week's schedule, it's the first one.