I get sub-arc hour at my location, occasionally, when I don't have 8/8ths stratus and embedded cumulo-nimbus. I am not at sea level either, I am proudly 12 metres above it, where it will make six-eighths of five tenths of nothing of a difference.
But, at my image scale and focal length, I can get pretty darned round stars. They might FORM a round star after pinpoint oscillating around for the 20 minute exposure, but hey, they are round!