What time of day did the columbine massacre happen?

The shootings at Columbine High School in Columbine Colorado on April 20, 1999 began at 11:14 AM when Eric Harris and Dylan Klebold placed two bombs in the cafeteria. They then went outside the building to wait for the bombs to detonate. When the time had passed for that to happen and did not, Harris and Klebold returned to the building, shooting their first victims on the way. They returned to the cafeteria and shot at one of the bombs to detonate it; the bomb went off and started a fire which was extinguished by the building's sprinkler system. The pair went through the building firing indiscriminately at whoever was there, ending up in the library where they committed suicide. From the time they planted the bombs to their suicide was an estimated 41 minutes.