Adding my "Delayed NTP" experience...
A relative was scheduled to connect yesterday on 1074, MDW-PHX, which was supposed to depart at 7:25PM and arrive at 10:15PM. Because of the
winter weather advisory I switched his routing but kept an eye on this flight.
Yesterday afternoon that flight, and its originating leg out of ALB, switched from being on-time to "Delayed NTP" and stayed like that for several hours. I checked automated flight info (option 1 at 800-I-FLY-SWA) during that time it stated an arrival time bouncing between 12:45AM and 1:45AM.
At about 9:30PM MST I had access to a computer and checked the flight at three sources. Southwest.com showed "Delayed NTP" out of MDW and "Delayed" at PHX. Automated flight info listed 9:55PM departure and 12:45AM arrival.
FlightAware listed 12:39AM departure and 4:09AM arrival.
When I was at the airport about an hour later to pick up my relative, the arrival board at the ticket counter listed a 5:30AM arrival time and automated flight info said the same thing.
FlightAware this morning shows that the flight arrived at 7:40AM (!!!).