I thought I would shime in and share a post I found from Entrepreneur
These stats are always good to know. If you post something outside a time frame, it's like aiming at the wrong audience (or a small percentage of the population). You might be wasting your time and money.
This article may be seen in a few months after it's been published through good SEO and keywords. Social media is very volatile.. you miss the time frame, you miss your chance to get noticed.
Here's a few exceptions to this time table
Twitter: People have a chance to share their own thoughts or retweet in the afternoon.
Facebook: The work day is slowing down and people have more time to do a Facebook check.
Tumblr: Reading micro-blogs on Tumblr takes more time and thought than other platforms, so non-work hours are often ideal.
Pinterest: Weekends are best, as the craft and collection emphasis of Pinterest lends itself to weekend projects.