Having executing hundreds of email campaigns, there was always much discussion around timing of the email send. Monday mornings - no. Friday afternoon - no way. Next Tuesday - no, we're sending an invite out for our annual user conference that day. Throw in coordination with other Marketing components and initiatives and pretty soon you need a complex analytic scheduler able to react to sensitive human input factors.
Well, just to make your life a little more complicated, I ran across this article, The Best and Worst Times to Post to Social Media (Infographic) from Entrepreneur Magazine around the timing of posts to social media. Yes, it's useful to consider and yes, it will drive you crazy as you now can try to coordinate these activities with all the other items on the agenda. Hopefully it pays off!