Let's take a worse case scenario: what happens to the ATF in a typical automatic transmission if you sit in one spot idling for an hour? Does the fluid not circulate well at idle? Would it circulate better if you increase the engine speed or does it have to be in gear to pump fluid better? How much heat is generated vs driving down the road? My concern is that if the fluid does not circulate well at idle, could the fluid in the torque converter overheat.