In order to get to the second floor break room where Truly and Baker encountered him, LHO would have had to leave the domino room, and walk across the first floor to the stairs. This would have had to occur immediately after the shots were fired in order for the timing to work out.
What do you mean by "In order for the timing to work out"?
It is nonsense. Oswald could have gone up to the 2nd floor lunchroom shortly before the shots were fired. I suppose this is where the bottle of Coke comes in. IIRC, Baker initially said that Oswald had the bottle in his hand, which means he had already been in the lunchroom long enough to operate the vendingmachine before Baker encountered him.
But that doesn't sit well for the 6th floor scenario and it would reduce the available time for Oswald to get to the lunchroom even further. That's why Baker scratched out the mentioning of the Coke bottle in his second affidavit. Without the bottle, he could claim he saw Oswald walk away from the dividing door, which of course would suggest he had just arrived there.