Better check your videocard driver's settings. For NVidia on Windows, you can for example alter number of prerendered frames which IIRC defaults to at least 3. Putting that to 0 and turning off a bunch of other things listed in the settings, decent nVidia cards on decent hardware can get a latency of 2 frames which is probably the bare minimum. At 60Hz with a screen which doesn't add additional latency that is 33.3mSec (between the software issueing a render call and the actual output on the screen).

At work we measure latency using an oscilloscope, a photodiode pointed to the (top left of the) screen and some input event e.g. from a fast digital output card (i.e. less than a mSec to get an output high from software). E.g. in software we set an output high in the piece of code of interest then just measure the time between that high edge and the photodiode firing. But using a camera is a neat though somewhat more manual process.