When billing hourly, I only bill when I'm actively working. Actively working can include continuing to think about the project while stepping away to use the bathroom, or "hammock driven development" that doesn't look like work to a casual observer but absolutely is.
It does not include stopping for lunch, spending 15 minutes on HN, or anything similar that definitely isn't work. Those kinds of breaks on the clock seem reasonable to me for daily or weekly billing, but not hourly.
It does not include stopping for lunch, spending 15 minutes on HN, or anything similar that definitely isn't work. Those kinds of breaks on the clock seem reasonable to me for daily or weekly billing, but not hourly.