You are already asking the wrong question. The proper question is:

“What is the best time to post an X kind of SM post on platform Y in order to reach my target audience of Z.”

Until you can state the kind of–for lack of better phrase–kind of engagement you are offering, on which specific platform, and which particular market demographic(s), there is no valid way to answer your question.

And, if you want to do it right, you will use different hooks to reel in different market segments in different SM areas.

I mean, you wouldn’t use fly fishing gear and lures to catch tuna off of Alaska, would you?

Pretty much the same thing.