Neither do you, of course.
It's up to each of us to determine for ourselves if it is foolish to believe Benavides sat in his truck for a few minutes while Tippit's body was lying in the street and others were already gathering around... or if Benavides sat in his truck for a second or two once the killer went around the corner.
Actually, on this one I agree with Bill.
And there is a way to make a determination of sorts about which of the two statements made by Benavides is more probable.
Callaway only had roughly 2/3 of one block to run to the scene, which would have taken him less than a minute. He started his "good hard run" after watching a man with a revolver running towards him on Patton and turning onto Jefferson. That man's run would have taken no more than a minute either. And we know from one of Bill Brown's YouTube video's that it took about 30 seconds to walk from Tippit's car to the corner of 10th and Patton. Add it all up, and the most probable conclusion must be that Callaway arrived at the scene roughly 3 minutes after the shots.
When he arrived, Bowley had already made his call, which lasted 48 seconds. In other words, Benavides had no more than roughly two minutes after the shots, to get out of his car, check on Tippit and try to call the dispatcher before handing over the mic to Bowley, which in turn means that his estimate that he waited in his car for several minutes can not be correct.