If you correctly read the transcripts you will know Williams did not eat his lunch at the southeast corner. And by his estimate he finished no later than 12:12 then went down to the 5th floor.
Mr. McCLOY. What time of day was this, when you were eating your lunch?
Mr. WILLIAMS. About 12.
Mr. McCLOY. Just 12?
Mr. WILLIAMS. Yes, sir.
Mr. BALL. Now, as you looked towards the southeast corner from where you were sitting, could you see the windows in the southeast corner?
Mr. WILLIAMS. In the Southeast is--the southeast. I really don't remember if I seen anything-- it would be just the top edge of the window, as I remember.
Mr. BALL. Did you see anyone else up there that day?
Mr. WILLIAMS. No, I did not.
Mr. BALL. How long did you stay there?
Mr. WILLIAMS. I was there from--5, 10, maybe 12 minutes.
http://mcadams.posc.mu.edu/russ/m_j_russ/jarman.htmMr. BALL. Where did you eat your lunch?
Mr. WILLIAMS. I ate my lunch--
I am not sure about this, but the third or the fourth set of windows, I believe.
Mr. BALL. Facing on what street?
Mr. WILLIAMS. Facing Elm Street.
"Mr. BALL - The sidewalk in front of the Texas School Book Depository Building?
Mr. JARMAN - Yes, sir.
Mr. BALL - How long did you stand there?
Mr. JARMAN - Well, until about 12:20, between 12:20 and 12:25."
Jarmin and Harold did not proceed to the 5th floor until after 12:20-12:25
Williams was not on the 5th floor when they arrived.
Williams said he did not leave the 6th floor until he after he heard noises coming from the 5th floor and took the elevator down to see if it was his friends.
Are you implying Oswald was lurking on the 6th floor in the "snipers lair" for 20-25 minutes, undetected by Williams only a few windows away?
Oswald could not have known when the President would pass the TSBD, but lunch was over at 12:30, workers would normally be returning to work on the 6th floor at that time. Something to think about.