[esalman]

They did- https://psychopy.org/general/timing/millisecondPrecision.htm...

> The stimulus presentation on MacOS used to be very good, up until version 10.12. In MacOS 10.13 something changed and it appears that a form of triple buffering has been added and, to date, none of the major experiment generators have managed to turn this off. As a result, since MacOS 10.13 stimuli appear always to be presented a screen refresh period later than expected, resulting in a delay of 16.66 ms in the apparent response times to visual stimuli.