I've worked in a web agency that billed by the hour. Clients would ask for justification on why something would take 5h of support instead of 2.5h because the

I've worked in a web agency that billed by the hour. Clients would ask for justification on why something would take 5h of support instead of 2.5h because the previous similar request was done in half the time during the development of the app. What they don't understand[1] is that if they ask for an urgent fix after deployment, they're going to pay for a developer that had free time this very moment to pull and install the project. That dev then need to read and understand the codebase, make the fix, test it, make a pull request, ask for someone else's billable time to approve the pull requests, merge any conflicts, schedule a release, push the release, test again and document the new feature. And that's if the request is in fact as simple as it look like. Often, requests look very similar but are very different to each other. "Why does it takes 3 hours to add a button on the sidebar while it takes 1 hour to do it in the content of the FAQ page?" Well, one is done by the content team and require no code or release. The other needs to be done in the code. Etc. [1] They are told in very simple words that this is how it works.