On Twitter, have 3 tweets, for example 9:00 AM, 2:00 PM and 5:00 PM. Make sure they are tracked, there are lots of basic tools that can help you track your tweets (Hootsuite, shortened links...etc). From there you can decide, which is a good time to post.
For Facebook, I would have one updates at around 1:00 PM. and ONLY one update...
The rest, it depends on the target audience and activity of the channel..
