I only ran the heater for a total of around 40-45 minutes. The hose was warm but I think the block rear was cold. It was 4-5 F outside. I trickle charged the battery today until fully charged. Based on the last few days, I'm pretty sure I can reliably start this tractor with a good battery and no heater down to 10F if I need to. To make things easier on the starter and tractor in general, I'll probably use the heater.
The compression release works really well and the oil pressure comes right up before starting. I like that feature.