The Bureau of Labor Statistics released an annual report tracking how much time Americans spend, on average, on various daily activities.
This year's report, released in June, shows that in 2013 Americans spent the bulk of their time doing what the BLS labels as "personal care activities." The bulk of those "personal care activities," however, is sleep. In fact, Americans spend an average of 8.74 hours a day sleeping (which the National Sleep Foundation would certainly approve of).
If sleep were to be excluded, "leisure activities and sports" would come out on top, with the average American spending 5.26 hours per day on such activities.
Work related activities come in third, with the average American clocking in 3.46 hours of work per day. It's important to note that, however, since most don't work weekends or holidays this doesn't necessarily indicate that the average American only actually works 3½ hours a day during the 9-to-5 workweek.