VERY little, if any, time to react, e.g. 100 to 150 feet, or about 1.5 seconds at 60mph. The way to strike back is to trick up your license plate. The radar jammers that really work will get you a lot more jail time than any speeding violation. They're unlicensed transmitters, so they're banned by governments world wide. They rarely live up to expectations of customers, so we don't sell them.
All detectors made in recent history are superhets.
This means they have oscillators which send out a weak, but detectable signal. Some genius decided to take advantage of this fact to make a product to sell to liberty loving governments the world around. He called it a vg-2. The cops hold this black box which simply detects the presence of a detector. Your defense is a detector with vg-2 shut down.