I see that the description of this env variable is
How long the old deploy will overlap with the newest one being deployed, its default value is 20. Example: 0

Let's say that I have this set to 120. During those 120 seconds of overlap, do requests go to the new or old instance at say, the 60 second mark? I did some searching around and see that there may be a 15 second delay due to dns/http proxy switching, but wasn't able to find a definitive answer.