It's probably around or below 100ms - that's the amount of time it would take a person to recognize that a visual change has taken place. It would take even longer for a person to determine what (out of all the things in their visual field) has changed . There would be variations in individual reaction times relative to age and cognitive ability. If you're looking at the screen out of the corner of your eye, you would be able to detect a faster change than if you're looking directly at the screen (due to the placement of the different kinds of photoreceptors in the eye).
There may be experimental information about this from a big search company somewhere who wants to know how fast a search result needs to return to seem "instant".