The interaction research that underpins loading design was written for a world where three seconds was a catastrophe. A reasoning model with a retrieval step in front of it can take forty. Every rule of thumb you inherited breaks at that scale, and the replacements have to be derived rather than looked up.
The three response-time limits
Jakob Nielsen’s Usability Engineering (1993) sets out three thresholds, themselves drawing on Robert B. Miller’s 1968 work on response time in conversational transactions. They have held up for three decades because they are grounded in human perception rather than in the hardware of any era:
0.1 second — the limit for the result to feel instantaneous, as if the user caused it directly.
1 second — the limit for uninterrupted flow of thought. The user notices the delay but does not lose their place.
