@pemile
https://www.firehouse.com/home/news/10539288/times-of-sept-11-attack-wtc-collapse

"...the precise moments eventually were established by a seismograph at Columbia University’s Lamont Doherty Earth Observatory in Palisades, N.Y., 21 miles north of the World Trade Center.

(...)

Here are the Eastern Daylight times, duration of impact and Richter scale magnitude :

• 8:46.26 : American Airlines flight 11 hits north tower, 12 seconds, 0.7.
  
• 9:02.54 : United Airlines flight 175 hits south tower, 6 seconds, 0.9.
  
• 9:59.04 : South tower collapses, 10 seconds, 2.1.
  
• 10:28.31 : North tower collapses, 8 seconds, 2.3.
  
• 17:20.33 : WTC building 7 collapses, 18 seconds, 0.6."