I think you're missing the distinction between "office hours" (what most people would read as 9-5 Monday through Friday) and "Office Hours", the term Simon is using to describe the 4-5 hours a week that he specifically allocates to having discussions with his users. Which is completely understandable given that there's not actually a consistent capitalisation difference.

Of course the latter is still time spent working on the project, but it's certainly not in direct conflict with having a full-time job paying the bills.