Your contentions require very punctual timing. Nothing about Markham’s account indicated that she was that punctual or paid close attention to the exact time or that the clocks she relied upon were entirely accurate. Neither were most people that punctual back in 1963.
We've been through this already. I agree with you, in general, that people do not keep acurate account of the time, but there are exceptions. If, like in Markham's case, you need to catch a bus at a certain time, you need to be punctual in your timing, or you will miss the bus. If, like in Bowley's case, you need to pick up your daughter from school and then your wife from work, you also need to be aware of the exact time to avoid having them wait for you.
The thing with these two witnesses is that by themselves they would not provide sufficient information to confidently arrive at a likely time of the shooting, but combined it is another matter all together. Even more so when placed in a wider context of interactions with others at the scene of the crime. So, let's look at what we know and see if you can follow along.
The most obvious indicator that Tippit was not killed at 1.14 or 1.15 is that the authorization for autopsy shows that Tippit was declared DOA at the Methodist hospital at 1:15 pm. DPD officer Davenport, who followed the ambulance part of the way and was present at the hospital confirms that time in his report.
And then there is the combined timeline of Helen Markham and T.F. Bowley that does not compute with Tippit being killed after 1:10 pm at the latest. No LNr has even tried to come up with a plausible scenario for Markham still being at 10th/Patton at 1:14 or 1:15 when she testified she left home "a little after 1" and the one block walk from her home on 9th street to the corner of 10th street and Patton would have taken her only 2, perhaps 3 minutes. Markham estimated in her testimony that she took the 1.15 bus to work every day, but according to the FBI the bus was scheduled to stop there at 1.12 and at 1.22. It actually doesn't matter which bus Markham was talking about, because a walk of two blocks to the bus stop would have taken her no more than 6 minutes. So, if she left home "a little after 1" she would have easily been at the bus stop at around 1.15 and thus not at 10th/Patton. In other words, Tippit must have been shot earlier than 1.15, most likely around 1.06, because otherwise Markham could not have witnessed it.
The same thing goes for Bowley. He arrived shortly after Tippit was killed. In his affidavit he said he picked up his daughter at R.L. Thornton School in Singing Hills at "about 12:55". School bells, in my experience, have a tendency to ring at the correct time every day! Now, let's also not forget that, after picking up his daughter, Bowley was also going to pick up his wife from work, to go on a family holiday and thus had every reason to be on time and be aware of the time! The drive from the school to 10th/Patton is about 7 miles long and takes roughly 13 minutes, depending on the route, making it absolutely possible and plausible for him to arrive at 10th street at 1.10 pm, like he said he did in his affidavit. But even if we accept that Bowley didn't pick up his daughter on time (leaving her waiting for 5 minutes or longer) and did not leave the school until 1 PM, he still would have arrived at 10th/Patton at 1:13, which of course would have been prior to the shooting of Tippit at 1:14 or 1:15, as the WC narrative claims.
The interaction of Bowley with Callaway further confirms Bowley's arrival at the crime scene shortly after Tippit was killed. He testified that he was about half a block away from 10th Street when he saw a man coming down the street with a revolved. After that encounter Callaway ran half a block to 10th Street and when he got there Bowley was already there, using the DPD radio. Both Bowley and Callaway assisted in putting Tippit into the ambulance which arrived only shortly after Callaway got there. The ambulance brought Tippit to Methodist hospital which was about two miles away (if memory serves) and Tippit was declared D.O.A. at 1.15.
This timeline fits perfectly together if the shooting of Tippit happened between 1.06 (the time Markham would have gotten to 10th street after walking one block) and 1.10 (the time Bowley arrived after having picked up his daughter from school). If you move the time of the murder back to 1.14 or 1.15, as per WC narrative) none of the timeline fits.
Eliminate the impossible and what you end up with, however unlikely, is the truth.