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> ~100ms represents optimal [human] reflex time in recent research.

For unpredictable inputs. Intervals between a human own actions or discrepancies in delays between successive external events can be effected or perceived with significantly greater precision, especially for people with e.g. music training, especially for percussionists. I’d bet on somewhere between one and two orders of magnitude more precision, that is single-digit milliseconds, at higher skill levels. (Chopin’s Fantaisie-Impromptu is among the easier rhythm-based parlour tricks and already requires staying below ~30ms of error. Alternatively, a single frame at 60fps is 17ms, and speedrunners can hit single frames of a game pretty reliably.)

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Reaction time is unrelated to perceptible latency. You're not reacting to things; you are seeing the result of an action you requested. You already know it's coming. To say that delays less than your reaction time don't matter is like saying it doesn't matter if your flight is delayed by an hour because it takes 8 hours to cross the Atlantic.
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Watching your own hand movements through your phone camera is a good demonstration of this. Set 60 Hz video mode, and the latency is probably less than 30 ms - but still extremely obvious.
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it's quite a lot more than 30ms, as phone cameras do some real heavy-weight image processing to compensate for their tiny size, I'm talking neural networks and such. the throughput might be 60fps when it's all conveyor-ed but the latency sure isn't
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You're right. Looks like it's more around 90 ms, at least for my iPhone 12 Mini. Test setup was taking a photo of the iPhone 12 Mini watching an incrementing counter on a 50 Hz CRT.
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If the animations are effectively 'cancellable', i.e. they don't block input or delay the change in state, this can be reasonable. You can put in a sequence of actions into a UI at a much faster pace than 100ms, if you have the muscle memory for it.
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