Time Line

By now we have all seen the end and the results. Fifty nine people are dead, 527 wounded, but where and when did it all begin?
In the military we had a thing called backward planning. Yes, I know, much of what the military does is ass backward, but that was not what was meant. Say I wanted to be in Sioux Falls S.D. at 10P.M. I would know that since the trip takes me seven hours I would need to leave prior to three. I would know I needed to make two fuel stops, and allow time for that. Since this is construction season, I would need to allow for detours and delays etc. We then continue with what to take etc, you get the picture.
Stephen Paddock did not on the spur of the moment decide he was going to slaughter a bunch of rednecks at a Country music festival, This took planning and much preparation.  Quite the task for a 64 year old man to accomplish alone. Or did he have help? We might never know.
To acquire the weapons, munitions, do the conversions, calculate angles and do the prep work would have taken weeks. My guess for a start date? Sept 12 2017 when he got his copy of What Happened?