You are way colder than I am too. But, in this case I am not sure I had a problem. Everything worked OK, but I just could not reasonably follow the instructions in the Owner's Manual which advises to not use the equipment until the hydraulic filters feel warm. It just was not going to happen within any reasonable time period.
My my utility tractor, JD 650, has no such owner manual advice and I just fire it up and work it lightly until it warms. I have the low temp JD Hytran in the JD and that fluid is similar or same as the good Kubota stuff, although not tinted orange. Hydraulics work normally right off the "get-go". The Ventrac is a different sort of horse, no real hydraulic "tank", the gear cases and front axle are the case and no good place to insert the heated dip stick as the fill port is the opening to a recovery bottle, like a coolant recovery bottle. The Ventrac has Ventrac hydrostatic fluid almost certainly Amsoil, which again is similar to Kubota's best stuff.
Mountaineer reported not being able to move if too cold, he is also in colder area than I, but not that much. If I were he, I would make sure the hytran fluid is the proper low viscosity stuff. For me, I think I will let it let it idle a few minutes to get flowing and then work lightly for another few minuted and then GIT"R DONE!
prs