If you message me, and then get upset if I don’t respond immediately, then that puts you in the position to imply that you are self-centered, and believe everyone should revolve around you. There will be times I will not be able to answer immediately. Instant Messaging implies that I will likely receive the message immediately – not that I will reply immediately.
When I am about to go to bed, my phone goes into a DND mode. I am still relying on the iPhone 14 which has a DND switch. When I am in the doctor’s office, or other important situation where I shouldn’t be disturbed, I will turn on DND. If my DND is on, leave a message and I will get back to you when I am available. If you are sending constant barrages demanding my attention, then that is just not right, and I may even not reply to you – or make you last. I am likely not the person you would call for emergencies.