I don't know why but I get replies within 15 minutes to 24 hors when I email delta. I am platnium but even when Silver I;d get my replies fast. maybe because of where I live in the Dominican Republic but I do have a friend based in NY who hasn't gotten a reply to a complaint from over a year ago.
I had a 8 hour delay on April 6th SDQ JFK emailed the 7th got a reply the 8th.