Overhead showing the west wall in 1963
The question is if that single white door exit on that west side was guarded by 3 min post shots as were the front and rear exits (per the WC testimony of DPD Barnett)
If that west side entrance is also being watched as early as Barnett says that plainsclothes officers were at the rear of the TSBD as early as 1 min post shots then Oswald cannot have gotten out of TSBD unless there is one modification in the timeline: Meeting with Mrs Reid in the 2nd floor office occurred at 60 sec post shots.
Here is timeline according to WC after Belin stopwatch time (his own imposition, as opposed to Mrs Reid herself estimate) of Oswald ENTERING the rear door of 2nd floor office at 2 min post shots, after having been seen by BAker in the lunchroom approx not later than 90 sec post shots.
It would have taken Oswald another 30 sec to traverse about 90 ft at 3 ft per sec which is the "slow" pace that Mrs Reid observed. Oswald was only in his T shirt, thus his brown shirt and or jacket that Baker had seen him wearing, was left in the lunchroom.
Oswald therefore exits 2nd floor office front door at 2 min 30 sec post shots. He then must travel back down an 80 ft hallway and about 15 more ft into the lunchroom, and about 5 sec at least to put on his brown shirt/jacket, . That places him exiting the lunchroom again at approx 3 min post shots and having to travesre another 12 ft across landing and down the rear staircase, puts Oswald not reaching the ground floor until 3 min 15 sec post shots.
At this point the rear loading dock exit and front lobby entrance doors are being guarded accordiing to DPD officer Barnett.
So the only possible door Oswald could have exited from, is that white west side door in the photo and given the 50 ft distance from rear staircase, not exiting it any earlier than approx 3 min 25 sec post shots.
If that exit is guarded, and the reporter named Peirce Allman who said he met Oswald in the front lobby after Allman went right in, early enough to not been stopped by Officer Barnett, = a meeting with Oswald at approx 2 min 15 sec post shots., then Oswald has an alibi and Mrs Reids meeting must have occured at 60 sec post shots( which matches her own WC testimony of her actions)