That's interesting 10 to 20% more time from 1st to 2nd serves. Were those numbers for only serve and volley points or all 1st and 2nd serves regardless of whether the server played serve and volley?
The latter would be a little more interesting number.
Those are all serve and volley for both first and second. The Laver numbers are from the 1969 Wimbledon final. I gave up trying to find serves where he stayed back, both him and Newcombe s&v'd pretty much every point. The Fed, Sampras numbers are from 2001, and I didn't find much difference in the times regardless of whether they came in or not.