I don't think I understand that quote. Is that Maugham saying you don't actually need inspiration so you can just sit down and work without it? Or is he sarcastically saying jobs are badly configured because you can't just sit down at nine o'clock and produce something good? It could mean either.

It's sarcasm. One possible interpretation is that money is a strong motivator, and writers generally don't make money by not writing.

I think it is the first - that he doesn't rely on the motivation, and instead uses discipline.

Also that discipline begets motivation. Exercise every day. Pretty soon you feel bad if you don't exercise.

I interpreted it as saying you can train inspiration to arrive, just like anything else, with enough discipline.

That quote will not help anyone. The question is WHY it strikes every morning at nine o'clock sharp? What do you have to do for that to happen? Because that inspiration is just an efect of previous actions.

Maugham is basically saying that it's discipline that matters. And once you do it enough number of times, it becomes so routine that you will automatically be able to write at the time you've set for yourself.

Yeah. What I want to add, from my own experience, is that you can have discipline (you show up) and still can't do anything (you are not prepared). This kind of dicipline in doing comes from discipline in preparing. At this age this could be even more important because we live in crowded cities that simply are not design for this.