Complex sentence: According to SAO Krajina sources, the air strikes commenced at 9 a.m. and took fifteen minutes, followed by 30 minutes of artillery bombardment before ground forces were ordered to attack.
Split into simpler sentences: According to SAO Krajina sources, the air strikes commenced at 9 a.m. and lasted for fifteen minutes. They were followed by a 30-minute artillery bombardment before ground forces were ordered to attack.