Earlier quoted context omitted.
I got fired from a job because I had done this and they couldn't figure out how to keep me billable after that. Well, I got fired because I would "show up late" and "leave early" because there was nothing else for me to do (even though I was actually pulling a full 40 hours, they were expecting 60 out of people). They could have given me more work, put me on new projects, etc., like I kept asking to be done, but inst…
Billing by the hour is basically just telling people how much effort you expect the task to require smoothed by how valuable it is to you. If you can do it quicker, I say bill the full amount of time and if they have extra inquiries, fit it into the buffer zone.
It means I'm not making as much as I could be, but it's not their fault I agreed to the arrangement 3 years ago.