As a software freelancer/consultant, I don’t sell my time, but my experience, my knowledge, and quality delivered solutions.
The current industry standard follows measuring and billing work by spent hours, which is really screwed up.
Hourly billing has more disadvantages than anything else — forces every side to deformed attitude. You are simply selling your time, no motivation to do stuff better, faster, to optimize your work, to analyze/think about other approaches (shortcuts), to be better craftsman ==> be more productive. And customers will have a tendency to question your work, to tell you how to do your job, “why…