We just ran across a great article with research on the best times and days to post in social media, broken down by platform. Better yet, it has an infographic for all the major platforms.
And yes, these are generalizations, because the research covers a range of categories and brands. And of course the causal relationship question comes up: are these the best days and times because the platform wants to reward those timings, or are these results based purely on pure, unadulterated human behavior? Maybe the positions of the stars?
Your best days/times could be different from what’s seen in the chart. Again, the cause question, because your best days/times (as seen in the insights provided by each platform for your brand) could be due to your unique posting patterns, brand, category or content. Who knows?
Anyhow, check out the article on Oberlo's blog. It's a good one. Also recommended: read the comments and engage in the conversation. That's really where the good stuff is.