Fast Company published a great article from Buffer featuring solid statistics on how often you should post to the various social networks your brand is present The article says it all, but I have chosen to highlight a few of the most important ones.
Facebook and Google +: Post once a day, optimally 5-10 times a week. Facebook posts reach their half-life at 90 minutes. A post reaches 75% of its potential in the first five hours.
Twitter: Tweet five times a day (small businesses). However, if you want to bring the most value out of your Twitter presence a s whole, tweet up to 30 times a day. A tweet has a 18 minute life expectancy, and reaches 75% of its potential in the first 3 hours.. 46% of customers expect a support request to be answered on Twitter within 60 minutes.
LinkedIn: 20 posts a month or one every weekday (this strategy reaches 60% of your audience).
Email: Statistics show that emails have the highest opening rate between 8 PM and midnight because they are more likely to stand out alone in your inbox.
Predict. Measure. Repeat.
Post when your followers are online and adjust for time zones.
Followerwonk is a tool that allows you to find find, analyze and optimize you Twitter presence for social growth. This can be used to determine when your followers are online and post accordingly.