Today I built and tested 4 thermostats and it took me well over 4 hours. Usually I'm faster, but an hour per unit is probably still a fair estimate.

Off the top of my head, I'd say it's somewhere around 130 solder joints. The new board design allows using Pi Zero 2 boards with pre-soldered headers. That that'll cut out 40 pins that I have to do by hand once I'm through my current stock.

If I sold more devices, I'd try creating a 3D printed jig to hold all the parts in at the same time. It just doesn't make much sense to do that when I sell so few units per year.