Human Perception of Slowness
in 1968 Robert Miller published his classic paper Response time in man-computer conversational transactions in which he described three different orders of magnitude of computer mainframe responsiveness:
A response time of 100ms is perceived as instantaneous.
Response time of 1 second or less are fast enough for users to feel they are interacting freely with the information.
Response times greater than 10 seconds completely lose the user’s attention.