I can understand Richard Smiths point about Oswalds 2 possible options to get from 6th floor to 2nd floor, but I cannot see how Mrs. Garner is refuted by suggesting the elevator trip is impossible.
The elevator trip is impossible only if you are absolutely certain that Oswald acted alone and was the 6th floor shooter.
There is the possibility of a small conspiracy scenario that one other person aided Oswald to use the East elevator by operating it to get Oswald from 6th to 2nd floor as soon as 50 sec post shots then the accomplice returns elevator to 5th floor by 70 secs post shots.
But because of the PM person appearing to be Oswald and the Hosty note contributing to PM likely to be Oswald , and the apparent sighting by Oswald of Norman/Jarman as they returned approx 12:25 and Carolyn Arnold’s 12:25 sighting of Oswald in the front lobby, Oswald becomes a low probability candidate to be the 6th floor assassin.
The East elevator scenario is more probable as means of escape for an unknown assassin and either a 2nd unknown accomplice or some other TSBD employee such as Jack Dougherty who was coincidentally in vicinity of 5th floor at time of shooting and he even admitted being on 6th floor just before the shots were fired.