[Jim Robinson]

How do they know the exact time of each event on the timeline?

[af_vet_1981]

Perhaps there were videos they synchronized with officer's devices.

Who Was Stephen Paddock? The Mystery of a Nondescript ‘Numbers Guy’

Learned two new points of data:
1. Girlfriend Danley attended Catholic Mass in Mesquite:
   
   Several days a week, she attended morning mass at a local Catholic church, said Leo McGinty, 80, a fellow parishioner who knew her from the casino.
   
   
2. Shooter refused to discuss Donald Trump with neighbor:
   
   Even more baffling, when Mr. McKay tried to strike up a conversation with Mr. Paddock about Donald Trump during the election campaign, he got no response.
   
   “Almost everyone has a reaction to Trump,” said Mr. McKay’s wife, Darlene.

[DoughtyOne]

Jim, my thought would be various sources.

The police scanner record of the event.

Media observations.

The live action and telephone captures at the event. Each are time tagged.

Then you have the officers reports, hotel staff reports, eye witnesses...

Perhaps someone else has a much better answer.