There is no easy answer to this question – it’s very individual and will depend on whether you are tweeting as an individual or as a business.
The joy of Twitter is that you get fairly instant feedback on whether you are tweeting at the right level. If you tweet too often, your followers will find themselves inundated with your tweets, and will unfollow you to help de-clutter their timeline. On the other hand, if you don’t tweet often enough, you may find your follower count stagnating.
What does the research tell us?
This wonderful infographic from KissMetrics suggests that 1 to 4 tweets per hour achieves the highest click through rate. But this is a statistical average, taking into account all those Twitter addicts who tweet several times a minute. There is a huge difference between tweeting once per hour and tweeting four times per hour - some of your followers might see once per hour as too little, while others see four times per hour as too much.
The more considered bloggers out there segment their Twitter efforts into tweets that engage their community and tweets that inform their community.
To inform their community through blog posts and news, the suggestion is to tweet about the post at least 4 times over a twelve hour period. Data from Sysomos suggests that 92% of retweets happen within the first hour of posting, so if you post only once then you might be missing loads of readers, because not everyone keeps their eye on Twitter all the time. The other advantage of this is you can experiment with different headlines to see which get the most retweets.
On the other hand, if you want to engage your community, then the advice is to tweet as much as you can afford time-wise. Focus on those that you decide are influencers in your marketplace and get to know them
Quality, not quantity, is most important.
One of the main messages though is to tweet quality rather than quantity. Listen and focus on your community – whether it’s your business community or personal network – and tweet and retweet engaging stuff, not simply to reach some magic number of tweets per day.
There are couple of tools that may help you to decide when and how often to Tweet:
TweetStats: shows you, using graphs and charts, how many tweets per hour, per week, and per month you’re currently sending out, as well as plenty of other useful stats.
TweetEffect: shows you which of your tweets gained and lost you followers. This can help you to understand whether you are tweeting too frequently.
Tweriod: analyses your followers’ profiles to indicate when would be the best time to tweet them.
These tools won't give you an answer to the question 'how many times a day should I tweet?' but they will give you information to help you find the frequency that works best for you.