How long does a freezer stay frozen when the power goes out?
I operate 5 inexpensive chest freezers 4 hours a day on a solar microgrid system. 4 hours is enough to keep them frozen hard, as long as they are full. I use water bottles to fill any extra space.If you put a lot of stuff in them at a time, they will need to be run overnight  (>12hrs) to freeze them down hard. If you do not freeze the contents completely at first, it may not ever freeze, because if it doesn't store the latent energy of freezing the freezer won't have enough thermal inertia to remain below freezing during the 20 hours of rest.On very rainy periods, we can go about 48 hours from the end of the last freeze cycle before any significant melting occurs.