Manhattan map

I'm curious, on the Manhattan map, they give you 5 seconds to fly out of the restricted area in a helicopter, and then you're killed. Who thought of that 5-second rule? Did anyone test it? Or did any other analysis to figure out how to do that?

It's impossible to turn a helicopter around and fly out of the restricted area in 5 seconds if you fly in during the heat of battle. Why can't they make it 10 seconds? 15?