Is There really an answer ?
The maximum delay between the image and the sound before it becomes noticiable depends on the sound and the image. If the sound or the video fades in or out, the delay is a lot harder to notice. I am pretty sure that it also varies from one person another.
As it is pretty subjective, people don't have the same results when looking for the acceptable delai.
Wikipedia says
For television applications, audio should lead video by no more than 15 milliseconds and audio should lag video by no more than 45 milliseconds. For film, acceptable lip sync is considered to be no more than 22 milliseconds in either direction.
The Media and Acoustics Perception Lab says
The results of the experiment determined that the average audio leading threshold for a/v sync detection was 185.19 ms, with a standard deviation of 42.32 ms
The ATSC says
At first glance it seems loose: +90 ms to -185 ms as a “Window of Acceptability”
and
- Undetectable from -100 ms to +25 ms
- Detectable at -125 ms & +45 ms
- Becomes unacceptable at -185 ms & +90 ms
To conclude
The results aren't so far from one another. It seems that the maximum acceptable delay is around 50ms, which is about 3 frames at 60 frame per second. If you have a delay, it should be the video that is delayed.