The fire truck is clearly shown in the footage. As far as I'm aware the truck arrived shortly after 1:00 PM.
There's no way to support the notion Oswald and Shelley were out front chatting until this time.
Spot on with the arrival time, Mr. O'meara, give or take just a few minutes to be fair. I'm sure the exemplary research of Mr. Davidson (Chris) could make a credible case one way or the other. Where I disagree respectfully with you is there is credible evidence to support the wrongly accused and Bill Shelley being together at this time in this location ---->
Don't have my notes handy at the moment, but lest we forget the wrongly accused told his interrogators,
*paraphrasing here based on memory from page 619 in the Warren Report... Mr. Bookhout (James, special agent w/the FBI) writes...
* "...he said he and Bill Shelley stood together outside for 5-10 minutes..."
We know from much closer examination that Bill Shelley akin to his work crew members shared a penchant for lying about their actual whereabouts and actions that afternoon. There's a reason for that. A hastily contrived script reared its deceptive head and any absolute genuine truth to the contrary of that "truth" was quickly avoided.
The wrongly accused wouldn't have used just any name to secure an alibi. He used the name of the individual he "stood outside for 5-10 minutes" with. It's a no brainer that Bill Shelley would lie about that. In fact, they all denied seeing the wrongly accused any time after his hasty escape (please excuse the eye-roll) because to do otherwise would mean the phantom encounter at 10th & Patton was/is the horse manure it is.
Again, if anyone is in contact with the widow of the wrongly accused (Marina Oswald-Porter) ask her in an objective manner if she recognizes either man in Mr. Mantesana's film to avoid leading her to a conclusion.