My brother sent this to me from a local newspaper remembering a drive-in theatre in Mesa. “It’s” is one of those words that does not follow the normal possession rules. The only time to use “it’s” is as a contraction of “it is.” If “it” owns something, it is simply “its.”
Plus, if you are talking about decades, they got it right the second time–the last two numerals of the decade, no apostrophe, and “s.” You wouldn’t spell it out once and then use numerals once.
Finally, “til” isn’t a word. It should be “until.” However, Merriam Webster and the Urban Dictionary disagree and say that “’til” is a contraction for “until,” but not in formal writing. That means that even though this wouldn’t be considered “formal” writing, this example is still incorrect since there is no apostrophe to indicate the “un” is missing.