You're metering, but at a lower level of granularity. You don't care about squeezing the maximum customer value out of ever hour, or maximizing hours you bill but don't do work in, because you're just not tracking hours. You work at an ordinary pace. Some days you're going to give your client 9 hours worth of productivity because you're in flow; sometimes they're going to get 7. It doesn't matter.
The only really important thing about your interval is that you can't book two clients on the same staffing in the same interval. If you bill daily, you as a general rule don't book two customers on the same day (really, I wouldn't do it in the same week).
