they had roughly 3 minutes to get him off that stage while they investigated who that person was on the roof
“In the video taken at 6:08 p.m. on July 13, the person appears on the roof of the building adjacent to where Trump is speaking and can be seen walking from the 1:00 second mark to about the 2:50 second mark.
Officials believe gunman Thomas Crooks, 20, began shooting with a collapsible AR-15-style rifle three minutes later, around 6:11 p.m. Counter snipers fatally shot Crooks shortly afterward, and law enforcement officials found eight shell casings near his body.”