I do consulting, but not as a developer, more business growth/strategy.
I tell all my clients, you are not paying for my time spent on a specific task, you are paying for access to my 25+ years of experience, learnings, and contacts.
An email that just says "OK" might be the net result of a set of experiences and knowledge that would take the client 2 weeks and $2,000 to obtain on their own. $75 would therefore be a bargain.
I've always thought that was weird. What is the underlying reason do you think? I get 6 minute phone calls, but to then pivot to another 6 minute+ task is too granular
Suspect 6 minutes being increment has more to do with being 1/10 of an hour (easy to calculate rate) & and as fine-grained as you can get without being so obnoxious you can't track.