What I meant by making yourself available is essentially sitting by the phone waiting for a call.
There are no recorded messages. So if you look at one of the examples in the article - looking for travel tips about a location - you ask your question and then sit around and wait for people to respond. You can't throw it out on your break and then close it down and go back to work while you wait for an answer, because you won't get one if you're not available to speak. On just about every other social media you can throw out a question or a topic and then not come back for weeks and still get your responses, if anybody had any.
In Elon Musk's case, he already has a huge following. So I'm sure he can get on whenever he wants to take part in something that pushes his brand and then basically forget about it until his next scheduled event if he wants to.
Maybe I'm missing something or maybe response times aren't really an issue, but it still seems to me like you have to be able to dedicate time to it like it's a meeting, rather than something you can do passively when you have a few spare minutes.