As far as I know, this doesn't exist; I apologize if it does.

Medialab/DirectRT could have a small timer utility that the research can trigger while testing an experiment, just to see how long it takes to run through it.
This could be achieved using separate timing utilities (a bunch of free ones should be available on the web).

Maybe this thing could also be used to write data for how long a subject took with the whole experiment when that information is useful (it probably isn't on most occasions, but still).