Passage: The four hijackers checked in for the flight between 07:03 and 07:39 Eastern Time. At 07:03, Ghamdi checked in without any luggage while Nami checked in two bags. At 07:24, Haznawi checked in one bag and at 07:39, Jarrah checked in without any luggage. Haznawi was the only hijacker selected for extra scrutiny by the Computer Assisted Passenger Prescreening System (CAPPS). His checked bag underwent extra screening for explosives, with no extra scrutiny required by CAPPS at the passenger-security checkpoint. None of the security checkpoint personnel reported anything unusual about the hijackers.Haznawi and Ghamdi boarded the aircraft at 07:39 and sat in first class seats 6B and 3D respectively. Nami boarded one minute later and sat in first class seat 3C. Ziad Jarrah called his girlfriend, Aysel Sengün, from a public telephone at the airport, repeating the words 'I love you' over and over. He boarded at 07:48 and sat in seat 1B. The aircraft was scheduled to depart at 08:00 and pushed back from gate A17 at 08:01. It remained delayed on the ground until 08:42 because of heavy airport congestion. The three other hijacked flights all departed within fifteen minutes of their scheduled times. By the time Flight 93 became airborne, Flight 11 was four minutes away from hitting the North Tower and Flight 175 was being hijacked; Flight 77 was climbing normally and was nine minutes away from being hijacked. By 09:02, one minute before Flight 175 hit the South Tower, Flight 93 reached its cruising altitude of 35,000 feet (11,000 m).With the attacks unfolding, air traffic officials began issuing warnings through the Aircraft Communication Addressing and Reporting System (ACARS). Ed Ballinger, the United flight dispatcher, began sending text cockpit warnings to United Airlines flights at 09:19, 17 minutes after he became aware of Flight 175's impact. Ballinger was responsible for multiple flights, and he sent the message to Flight 93 at 09:23. Ballinger received a routine ACARS message from Flight 93 at 09:21. At 09:22,...

Question: What time was Ballinger's warning received?
09:24