How does Zorz Studios define all-day sessions?

You advocate the all-day sessions a lot in your blog. How do you define them?

The beauty of our all-day portrait sessions is their "all-you-can-handle" approach so there is no limitation other than our endurance and a bit of common sense.

One point, though: you cannot break it into two (say, with a nap for a few hours) without paying for two separate sessions.