It's a question I've battled with, and one I continue to evaluate on a day-to-day basis. My feeling is that Social Media should complement the writing, not distract from it, but that's easier said than done.
This article has some helpful tips on this very subject:
HOW TO: Deal With Social Networking Overload by: Alexandra Levit
"As a career and workplace writer, I get asked all the time: I feel like I’m on social network overload"...(read more).
In this new publishing environment, platform has become an integral part of getting published. Robert Lee Brewer, Senior Content Editor at Writers Digest, has been guiding writers this month through the steps of building a platform with his April Platform Challenge. Writers are working to setup social media channels, connecting to other writers, and also working on developing goals and time management. So what is the right balance between social media and writing time?
So, it's an individual choice, one that each writer must decide for themselves. The best thing we can do is build a following of peers, industry mentors, and potential readers while also maintaining a consistent writing schedule. But if the book never gets written, it will all be for naught - balance is key.