Even assuming she was not commuting to work (sleeping at the office), that leaves 5.4 hours a day for eating, sleeping, shitting, showering, brushing your teeth etc. Nobody can do it for more than a week or two.
There are a very few people who can, or can come close. They can make life miserable for people who work for them, merely by being an example.
In an NPR interview with the woman who wrote Why Women Can't Have It All, the woman said that Hilary Clinton limits her time in the office for precisely that reason, so that people don't stay in the office merely because Clinton is there.
