In my experience that depends a lot on the size of the line coming from the engine to the gauge, and the length. Also temperature can play a big role. In general, a longer line will delay the reading longer than a shorter line, a smaller diameter line will delay the reading longer than a larger diameter line, and cold temperatures will also delay the reading longer. For my cars which generally use a #4 AN line about 5 feet long, in the summer the response is 1-2 seconds. A while back I had one of those small copper lines with lots of twists and turns in it, making it about 8 feet long, and that one would take up to 4-5 seconds to show movement in the summer. Also, the needle didn't move up the scale very fast with that one; might take 10-15 seconds to reach 50-60 psi.