I am not surprised or in awe that he is putting in 16 hours a day. Every passionate founder would likely be doing it. I am sure most of us have heard Steve Job's on how building a company is usually a 18x7 work-week.

What I am in awe and admiration is that he is managing two companies and in this case two completely different ones by nature! A rule generally accepted in the startup land is that you don't work on multiple ideas, in order to stay focussed on building one thing well. While twitter is not a startup (any longer) and Square is probably a very big/late-phase startup (if we can qualify it as that), they both definitely need the caring and nurturing of a founder (IMO). Given that, it is remarkable he is able to do the context switch needed to run both the companies. I would love to know how effective his leadership is, in both these companies, given that he isn't there longer than a typical day in either of them.

I am so tempted to try doing more than one thing, but then since I am a coder, I guess its not easy to digress daily as he can.