I think a full movement re-enactment would be very interesting..
From the 2nd floor encounter onwards.
http://jfkassassination.net/parnell/chrono.htm
In 90 secs, he purchases a Coke ... he has finished the Coke by the time he gets to the bus.
90 secs is a very long time to operate a vending machine with just one product to select. Try holding your breath for 90 secs or see how far you can walk in 90 secs. I can heat a can of beans in my microwave in 90 secs. Getting a coke? I'd say less than 20 secs even in a clunky machine.
How long does it take to point in a general direction and say "over there" or WTTE? I could do it without breaking stride.
How do we know that he finished his coke?
How do we know that he didn't jog part of the way from his rooming house? No one reported seeing him walking, crawling or sprinting. Maybe there was something on TV that would explain why he seemed to go unnoticed.