How do you justify spending time on social media in companies where management isn't onboard?

There are no justifications. It depends on the company policy to prevent or allow employees to access social networking sites like YouTube and Facebook. For an example, Mercedes and Chevrolet Egypt do not allow their employees to access social networking sites.

And although there are many reasons why social media campaigns fail, far and away one of the biggest reasons for failure is the lack of top-to-bottom “buy-in” from all employees in a company.

Tough question, It's really hard to explain if your company has a policy against social media use in the office - which I think is irritating - because really you shouldn't be creating that type of work environment.