I meant that the interviewer expects you to start answering after 3 seconds. Of course you can elaborate over (tens of) minutes. But that's very far from actual work, where you have time to think before you start solving a problem.

You may say "yeah but you just have to think out loud, that's what the interviewer wants". But again that's not how I work. If the interviewer wants to see me design a system, they should watch me read documentation for hours, then think about it while running, and read again, draw a quick thing, etc.