My general response is most maintenance work (responding to posts and requests, sharing, pinning/re-pinning, and re-tweeting, etc.) can be done in less than 20 minutes per day. However, to do this, one must set aside a larger chunk of time during the week (Sunday afternoon?) to schedule posts in advance.
Create a plan: what will you discuss/post for the next week? Will you post photos, tips of the day, blog or article links? Collect all your information, and check that your links are correct. Use a link shortener if necessary: bit.ly and ow.ly are easy tools that are free and can track your links.
Use a scheduling tool. Facebook has a post scheduler right on the status update bar, and it is very easy to review and/or edit scheduled posts from the Activity Log. Hootsuite.com is an effective tool that offers several packages; the free plan allows users to manage up to 3 social media sites, which is generally sufficient for most business owners and professionals. And then there is TweetDeck, another free tool that integrates Twitter with other social media sites.
Go old-school: use a timer! Don’t spend any more time on social media sites than you really want. Social media is meant to be just one of the tools in your marketing tool kit, and it is meant to be FUN! So, take those online relationships offline, and enjoy your life!