Automatic transition check level while running hot or with motor off ???

I am trying to find out if I check my trams level with the motor running or motor off. My 03 Tacoma pre runner v6 has undergone a new water pump and timing belt R &R as well as a new radiator and u joints as well as a new alternator plus center bearing and after I completed all this work myself I still can't find the answer to my simple question of whether or not to keep my engine running or not whil checking my trans level hot for acuracy????