What is a day? Most people would tell you it's the 24-hour period from midnight to midnight. But we also think of it as any 24-hour period; if you were awake from 10 AM one day until 10 AM the next, then you would tell people that you were awake for a whole day.
More than that, many people who stay up past midnight do not consider it to be the next day until they go to sleep and wake up. And this is where we return to the introduction.
If you don't consider a day to have ended until you went to sleep, but you also consider the day to be a 24-hour period of time, then you can, in fact, sit down one day for seven days.