Sorry, can't help you, but I left my 710IS in the glove compartment all night 3days ago as well - temp was in the (low?) 20s. Also that morning, I had to use it for several minutes outside in similar conditions. I have been too busy to try it out since but this thread isn't feeling me with confidence
. I have no idea how long Canon's warranty is, but I am right at the edge of 90 days as I bought the camera right after thanksgiving I think, so I may still have a safety net.
According to the Canon website, the operating temp range for both cameras is 32-104°F/0-40°C. I realize this info is of little use to you at this point, but it may help someone else...
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H