Based on the accepted timeline, Lovelady/Shelley have :35 to get back to the far corner/Stairwell on the TSBD 1st Floor. And Lovelady is Not even facing the TSBD at the beginning of this :35 second mark. If I am to accept they went through the TSBD front door, the timelines have to be reset/extended. I do Not believe we are seeing Officer Baker running across the Island at :20 Seconds after the kill shot. These timelines have been Quickened/Manipulated in order for Officer Baker to glimpse Oswald on the other side of the vestibule door leading into the 2nd Floor lunchroom.
35 seconds to get towards the back of the first floor is loads of time.
From the lobby to the area near the elevators is covered in 20 seconds at a normal walking pace.
That leaves 15 seconds for them to get from their positions in the Darnell pic to the front door.
It would take Lovelady 3 seconds to get from his position on the steps to the front door, it's a few steps!
They could spend another 10 seconds listening to Gloria before they made it towards the back of the first floor, easily.
You've not really thought about this.
There is absolutely no need to extend any timelines.