Why not? It can handle it.10F here and supply temps are 95F (edit: 90.6F - I'm an idiot and was looking at a temp in memory) with no issues but clearly starting to lose the ability to produce maximum temps (previous supply temps were 99-100F). It also almost immediately went into stage 2 and it took about 20 mins to reach set temp. We had 7" of snow yesterday and felt the cold air during a defrost cycle and went to the window to watch. Within 2 mins there was steam coming out of the top of the outdoor unit and you could watch the snow melt within a min or two on the top and sides and even on fan blades inside. Do I dare go to 5F?
The defrost cycle does suck as it is basically turning the AC on in the middle of the winter for 5 mins. The entire house drops 1-2F during that time and you can really feel the cold air during that time which is about 5 mins at 10F. I think it is not timer based but based on temp of the outdoor unit.