Dennis many thanks for your work. On your chronology you have the discovery of CE142 just before Day leaves the building with the rifle at 2pm.
I am unsure how you have placed this discovery at this time.
The only clue that I can find as to the sequence of events is the following comment by Johnson.
Mr. BELIN. You were standing there when he picked it up?
Mr. JOHNSON. Yes, because the Crime Lab was already finished where I was, and I had already walked off to where he was.
It seems that the bag was discovered after Johnson had entered the SN after Studebaker had finished dusting the pop bottle and lunchsack close to the 2-wheeler. This would have been after 2pm when Studebaker returned to the SE corner.