Two questions about working with concrete mix

One corner of my back porch foundation has crumbled to the point where I had to put in a temporary fix, a 2" x 8" board hammered into place under the outside joist which is holding it up fine - for now.
However it will need something more permanent and I'll get a heavy construction tube, put it in position and fill it with stone mix concrete. This is the kind of stuff that comes in the 66 lb. bags at Home Depot.
Two questions - what's the coldest temp. that concrete can withstand to set properly? I'm in southern Ontario and have doubts that our nights are warm enough yet to prevent freezing.
Second question - how long does the concrete need to cure thoroughly before it can take the weight of the porch?
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On Apr 6, 2:43 pm, snipped-for-privacy@home.com wrote:

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On Apr 6, 2:43 pm, snipped-for-privacy@home.com wrote:

The bottom line is that concrete should not be allowed to freeze for at least 48 hours after it is poured. And since it generates heat as it cures, the temp would have to go well below 32 F for freezing to occur. However, keeping something like a sonotube warm should be a small matter and you might as well play it safe. Throw an old blanket, straw, cardboard, or anything like that over the tube and you will have no worries.
It would probably be fine to set the porch on it after a few days, though if it is a lot of weight, let it cure for as long as you can--7 days or so? Why risk it?
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Thank you, Marson, just what I needed to know. Much appreciated.
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