I would like to be sure I understand your question so let me paraphrase it:

You would like to run your session at 60Hz--it's very important. So you would like some way to check that it's actually doing this while a session is running.

Is that correct?

If so, there are two ways off the top of my head. First, you can check the data in the log file. All of the display times for each stimulus are listed. If you are running the session at 60Hz, then every thing that is displayed must be on the screen for multiples of 16.67ms, about 17ms. So divide all the display times by 17 and see if you get an integer value (i.e., little or no remainder). That would be a good sign. Similarly, if you were running your session at 100Hz, then your display times should be in multiples of 10ms, and so forth.

It is more complicated, but another test is to use an oscilloscope. That can show you, definitively, what refresh rate is being used at any given moment in your experiment. It's a great way to independently validate the exposure times you have requested.

Hope that helps!