Multiple hourlong naps may add up to five hours. But they will rarely make you feel as though you have gotten a five-hour night of sleep, particularly during an eight-hour overnight shift.
Doing the work on schedule, with care, and to specifications doesn't guarantee that anyone will like the work or ask you to work again.
The meat plus the potatoes plus the salad in front of you may fill the plate, but may not fill your stomach.
What you earn this week plus what you earn next week should cover the bill you have to pay the following week. But freelancing doesn't always produce the paycheck you expect. And life tends to produce one more bill than you expect.
One hour of cleaning plus one hour of cleaning does not necessarily yield two hours of clean.
Math is one thing, but life is quite another. And sometimes, in life, two plus two really does equal three.