You should do both cold and hot. Start your sled up, let it run for 30 seconds, shut it down, and test (throttle should be at least partially open when testing). Start it again, let it get to operating temperature, shut it down, and test again. Pull until the gauge stops moving (it's a bit easier pulling if you remove the plug on the side that isn't being tested). Difference between cold and hot test should be no more than 10 pounds, and ideally no more than 7.
Not being familiar with Polaris, I'm afraid I can't tell you what your compression should be.
Hope this helps, good luck!