Earlier in the year our friends at fuseworks studio posted an infographic based on research from our colleagues at Buddy.
While this is a handy guide, the important thing to remember is that these guides form as a baseline from which to work. Your audience is not all the bazillion twitter/facebook users. So its important to include a measurement process in your regular reviews to look at when your content is being most effective. If your product is targeted at youth, you might see an uptick during school breaks or travel time, for working professionals it might be the start of tuesday.
I've been talking with Tom Webster of Edison research who is speaking at Dreamforce (plug) in my session How to Derive Insight from your Social Media Data. He talks about the importance of a research methodology in looking at social media data, its interesting and it applies to all users thinking of using social media data. Here is a recording of a webinar Tim did with us earlier in the year by way of a preview.
Here is what the Buddy study found (everything sounds cool when preceded by "Buddy").