How long did the Columbine Shootings last?

49 minutes

They had bombs that were set to explode at 11:14 a.m.
They started their shooting spree at 11:19 a.m.
11:42 a.m the last shot was fired at a person... OTHER THAN the two personal shots Harris and Klebold used to take their own lives.

It lasted for 28 minutes.