Did the front desk get any calls about someone smashing the huge windows before the shooting? If people inside the hotel heard the shooting, they SURE AS HELL HEARD THE WINDOWS BEING SMASHED BEFORE THE SHOOTING.
I doubt he smashed the windows and then took a break, watched a little TV and relaxed for a bit.
The gunfire most likely started within seconds after the windows were smashed which means anyone calling about broken glass would've been calling in the middle of all the pandemonium.