What's the maximum time the grid can go down until the frozen food is unthawed/inedible? 1 Day or less probably?

4 days after a tornado, the food in our chest freezer was still half frozen. We cooked up a good fraction of it and tossed the rest. But only because refreezing it would have caused freezer burn. In an emergency, freezer burnt food is better than no food.

The key was that we never opened the freezer while power was out. Regularly opening an unplugged freezer would have melted things a lot faster. Chest freezers also do much better than fridge freezers.

Thank you very much, was really not sure how long a frozen but unplugged freezer would last.

The bigger the freezer, and the more full of frozen stuff, the longer it will last. Bigger freezer because the volume to surface area ratio is larger, and more full because there's just more thermal mass at a low temperature to buffer any heat leaking in.

Let's say 12 hours? I've had it last longer than that but in the scenario I'm thinking about there would be rolling blackouts on the order of hours, not days.