Do you use scheduling software to manage your professional social media? You should! My favorite is the exceedingly user friendly Hootsuite. It's free and takes a lot of the burden off of you to get to your Twitter account three times a day.
With Hootsuite and its ilk (another is the notoriously buggy TweetDeck), you can schedule Twitter and Facebook (and even blog, if you have Wordpress) posts out into the future. So you can maintain a presence without interrupting a busy work day every 3 hours.
But when should you schedule? You want to find that sweet spot where your audience's eyeballs are actually on their own social media--otherwise you'll just end up too far down the Timeline. Hootsuite has an auto schedule feature that claims to monitor when you get the most interaction and help schedule posts at those times.
I'm skeptical of automating to that extent. The goal isn't to completely check out from your audience, just to take some of the pressure off. You should know when your audience is active because you're evaluating what gets a response and when. Still, it's something to try out.
Also look at this cool infographic, about when social media as a whole tends to be most active. I was very surprised...anything surprise you?