Markham more than likely missed the 1:12 bus plenty of times and caught the 1:22 bus without even knowing the difference. Why would I suggest that? Because she estimated the bus was scheduled to be there at 1:15. And that is evidence enough to convince me that Markham didn’t pay as close attention to the time as you suggest.
Your “impossibilities” are not so.....
Markham more than likely missed the 1:12 bus plenty of times and caught the 1:22 bus without even knowing the difference. Pure speculation and of no relevance to the timeline I have presented. Markham estimated that she took her regular bus at 1.15. That could be the delayed 1.12 or the 1.22. Either way - and that's the main point - she would have been at the bus stop on Jefferson at 1.15 and thus not at 10th street.
Why would I suggest that? Because she estimated the bus was scheduled to be there at 1:15. And that is evidence enough to convince me that Markham didn’t pay as close attention to the time as you suggest. I guess you missed it, but I have already stated that Markham's estimate by itself wouldn't be enough. It needs to be looked at in combination with other known facts.
Bowley arrived at 1.10. He looked at his watch! Bowley confirms and corroborates Markham's timeline in as much as that the shooting had already taken place prior to his arrival. So, for the timeline to be wrong, not only Markham needs to be wrong, but also Bowley. But then, Callaway said he heard the shots, saw a man running towards him, then ran half a block to the crime scene and when he got there Bowley was already there and working the police radio. So, Callaway confirms and corrobarates Bowley's account. Both Bowley and Calllaway helped to put Tippit in the ambulance, which arrived at Methodist Hospital at 1.15, which in turn is confirmed and corroborated by Detective Davenport, who followed the ambulance to the hospital.
With all this in mind, your dismissal of Markham isn't very convincing. Come back to me when you have a plausible alternative for the entire timeline and not just a part of it.