Before you start posting to any social media site, you should take some time to understand the expectations of its current users. Social media communities are all different, and each of the popular social media websites are a unique community with distinct differences.
Twitter users, for example, don't mind seeing your posts several times throughout the day. Twitter streams are so full of messages that fly on and fly off your screen so fast that you can miss most of the updates one of your followers posts and you won't miss a thing. You can always go back and review those posts if you want.
Facebook is a little different. You want to stay relevant and visible, but not post too much. Typically one to two posts per day can be enough for Facebook.
LinkedIn users, on the other hand, expect that you'll be too busy to constantly post to your LinkedIn profile. On LinkedIn, a couple of times a week is generally enough.
So to answer the question, there's no definitive answer. Post to your social media accounts as often as you have something useful to say, but keep in mind that each community is a unique community and has its own set of standards and expectations. Learn what those are and see how you - and your unique business message - fit in, and you'll find the recipe for your social media posting frequency that works right for you.