That depends on several factors, not just the ambient temperature. Important factors such as the relative humidity, wind speed, exposure to sunlight or shade, etc.
Here, where the daytime temps are around 100F, or a little more, while the sun is out. And the relative humidity is usually in single digits, at the same time. I sometimes have combs, with eggs, out of the hive for 10-15 minutes. So far, most of those eggs have survived their exposure, but I haven't really tested them to see how much exposure it takes to kill them. I'm doing my best not to kill them.