When using an atc meter, does auto temp compensation mean it is adjusting the reading to show what it would be at room temp if you are taking a sample at mash temp?
No. ATC only corrects the temp sensitivity of the probe. It cannot correct the ph change dependent on room temp wort compared to mash temp wort. Also if you are using your ph probe in hot wort it significantly reduces its life span.
I normally let the sample sit or chill it down in a freezer to approx room temp before checking. So with this meter I should be looking for 5.2-5.4 at room temp?
Anywhere from about 5.2-5.8 is fine. 5.5 is pretty standard.