Well normally you want to apply plastic filler over warm metal and temps, but seeing as this is only temp, and considering your stuffing a hole with the stuff anyways. Use a good amount of catalyst in the bondo, and you can help cure it with a heat gun, heat lamp, or even possibly a hair dryer. Also could use them to warm metal before applying it.
The actual air temp isn't as important as having metal warm and keeping the metal warm to help the filler kick.