A rather blurry shot through a window, inviting one and all to come hear some jazz—but only on Tuesday’s. Why that apostrophe, you might ask? (I hope you ask.)
Because “Tuesdays” ends in S, and some people have a compulsion to throw an apostrophe into every word ending with an S, even when the word isn’t possessive.
It’s just an ordinary plural, people. Curb your apostrophe mania, I beg of you.