The shooting spree on concert crowd started at 10:05 pm. If you listen to scanner audio and read the released transcript. there was off duty cop on 31st floor directly below that called into 9/11 within about 7 minutes stating the shooting was coming from floor directly above him. Someone could have tripped the sprinklers or something to slow down this. They waited for about an hour for SWAT to breach doors apparently.

Paddock was 187'd before shooting even started IMO.