Sure it is. As long as the toilet works when you need it, you (a) don't actually have to check, and (b) the plumber is free to sequence their tasks in an optimal fashion.
The message from the plumber is based on the assumption that the default state of things is that the plumber has not done their job and things don't work. If you feel like that's the default state of things, you should choose a different plumber, not ask for notifications about which things don't work.
kqr: "Hi Mr. Plumber, could you let me know when 3-->4 happens. I need to use it once you're done, but I'm busy and don't have time to micromanage or continuously observe your work on the toilet."
(plumber's gaze narrows) "No. Fuck you, kqr. Fuck you, I'm not telling you jack shit. I have rights and dignity as a professional."
kqr: Wow, what a great plumber. I'd hire that person again.
>kqr: "Hi Mr. Plumber, could you let me know when 3-->4 happens. I need to use it once you're done, but I'm busy and don't have time to micromanage or continuously observe your work on the toilet."
plumber: Done sir! Your new toilets ready to go.
(6 months pass during which time the plumber completed some other work that was done satisfactorily and approved by the client)
kqr: I'm trying to decide whether I should keep using you Mr. Plumber. Please write me a few pages summarizing all the work you've done for me over the past 6 months. Make sure you emphasize how it has helped me move my KPIs, and how it helped me look good to my wife. Make sure talk about how the work you did contributed to our objectives as a family. Also make sure to add a bit about how you have developed as a plumber over the last 6 months and how you plan to continue to develop over the next.
Also, please write down what could you have done differently for an even greater impact to the KPIs. Don't hold back, it's important for you to reflect on your past decisions and make sure that next time you don't miss out on any opportunity to improve the toilet maintenance process when you're faced with similar situations.
If my toiletry needs were large enough to hire a plumber to spend 40 hours a week in my home, I would not expect the plumber to tell me when the toilet works again. I would expect the toilet to work, period.
Clearly, I would have two toilets for redundancy (much cheaper than 40 weekly hours of plumber time). In the rare occasion when both are broken at the same time I would expect the plumber to volunteer that information. The brokenness is the exception, the workingness the default assumption.