What time is best to publish an article if you want the most exposure on social media ?

The answer to that is: It depends on the time your influencers are active on social media. There are a lot fo tools out there that analyze and suggest the best times to post (on social networks) based on your influencers on these social networks. 

Use that timetable to post your blog articles as well. There is the obvious yet one of the best tools called Buffer App that you can use to analyze 'best time to post'.

This can be seen easily by looking at the insights / stats of the pages you are managing. Your potential customer will be available in the high hours during the days as shown in your insights graphs of user activity.

I hope this helps.