You're talking about Nielsen thresholds, and the limit for "instantaneous" is actually ~100ms.[0] Anything slower is considered to have taken some time.

Now, if that wasn't depressing enough - the Nielsen research is from early 90's. In the intervening 25 years, the users have certainly not become any less impatient.

0: https://www.nngroup.com/articles/response-times-3-important-...