It nearly goes without saying that you're doing this on no budget and on your own. To maximize your time spent on social media, you must first decide what your goals are. Otherwise, you'll be setting yourself up to really be wasting your time. The next step is to create a game plan, using your marketing calendar as a guide. Stick to it. It will help keep you organized, keep you from frittering away minutes that can add up to hours and help keep your content fresh on a regular basis. Identify the two or so social media sites that your customers use, and focus your efforts only on those. Figure out the kinds of posts that give you the most bang for the effort, and make the most of them.
You mentioned HootSuite as a social-media management tool. This can help you schedule posts ahead of time and streamline your efforts. Others include TweetDeck and SproutSocial. You can also use the Facebook's own scheduling tool.