I had a meeting yesterday with an author who was reluctant to start the "Online Stuff" because it felt to him like a time drain (although by any standard he was very open to the stuff, just had questions). We talked through some tools, like Hootsuite, that can make your social media life fit right into your life-life.
By spending 30 minutes once a week pre-scheduling tweets using Hootsuite and Facebook posts, you guarantee that those channels will be active even if you get busy. It also frees you up to scan your accounts a couple of times a day to find someone to talk to or retweet organically. So you get the best of both worlds: content without having to devote time each day with real-time content as you've got a second.
Try out some of the tools out there. You'll find they make social media accessible on any time budget. MediaBistro's daily email has great news when a new one comes out.