Productivity soars when a system responds within 400ms. Below that, interaction feels instant.
Confirm the visual response lands inside 400ms. Otherwise add a loading or optimistic state.
When results render in under about 400ms, people stay in flow and refine their query live. They treat search as a conversation. Past that threshold they stop, wait, and lose their train of thought. Instagram's “like” is the same idea applied to actions: the heart fills instantly and the network request syncs in the background, so the interface never makes you wait to feel responsive.
For deliberately weighty actions like submitting a payment or deleting data, a brief, honest pause with clear confirmation builds more trust than an instant, ambiguous “done”. Speed is not always reassurance. Sometimes a moment of visible work is what makes an action feel safe.
A settings toggle waits for the server before it flips, so for ~700ms after a tap nothing moves. Users assume it missed and tap again — silently undoing their own change.
A search screen returns in ~600ms but hides it behind a centered, blocking spinner. The wait is short; the frozen screen makes it feel broken.