> Those numbers go back to the studies Jakob Nielsen did at the Sun Microsystems usability lab and the results posted in his oft cited AlertBox articles from 1993 and 1997...

Actually, Nielsen indicates that had already been a consistent finding for ~30 years at that point, citing “Response time in man-computer conversational transactions” (Miller, 1968) [0] as the original source.

[0] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Resp...