Back in the '60's I had my Pentax S1a body freeze up after an hour or two in -27 F below. It warmed up enough after an hour or so in a hotel room, to start functioning again. At the time, I was working in the province of Saskatchewan, for a publishing company and I needed to get photos..
I've lived in Western Canada (prairies) all my long life, where we get real hard winters.
Four hours out at -28 or colder....you're pushing electronic...or mechanical equipment at these temps.it. Nothing functions too well at these temps, including us.
If I'm out at these temps, I usually try to shoot from the comfort of a vehicle and at these temps...if you're in isolated territory, it's wise to keep the vehicle engine running.
The voice of experience has spoken.