If your contractor gives you a guarantee on the cracks, he isn’t a concrete contractor. The only guarantee with concrete is that it gets hard and it cracks.
I guess my point is that a patio is a largely decorative pour of concrete. There isn't much point if it looks like crap a few months after it is installed. If I paid for a patio and it developed large cracks very quickly I wouldn't be very happy about that, especially if I thought the issue was that it was poured with insufficient precautions when it was too cold. Most of you think that it won't be too cold so hopefully that won't be an issue.
It seems like this is the contractors decision to pour the concrete in the expected weather. I would expect some kind of assurance that the final product will look good for a reasonable period of time. What is the point of going to all the trouble and expense of a new patio if that is not the case?
The poster didn't say how large the patio is and if there are planned seams and expansion joints etc. If the contractor knows what they are doing and the size of the poured pads is small enough, then the pads should be free of large cracks for a decent period of time. This assumes that it was adequately dug out with proper base material, well compacted, etc. If this is one large pad and is so large that it cannot be expected to not crack fairly soon, then the contractor should make the owner aware of that and possibly suggest a solution different then poured concrete. If the owner doesn't care about cracks, then why should anyone else.
They really don't do concrete patios around here because of all the frost and the 100+ degree yearly temperate variation. Patios here are relatively small 2" thick paving stones with the seams filled with polysand or nothing. The sidewalks are poured concrete but they don't go larger than 6'x6' for each pour and every 5th pad has an expansion joint. These hold up very well and generally go a decade or longer with no visible cracks, excepting annoyances like tree roots and the narrow spots next to utility poles.