To put this issue into an easier to interpret format, I made a GIF of the Darnell film and as can be seen, the Motorbike cop who is Haygood is on the move and covering a lot of ground quickly, and the other Police Officer who is supposedly Harkness isn't stationary but simply came up to the bollard boundary and turned around and equally moved away at speed.
And let's remember that Dealey Plaza isn't very big and the distance covered by Haygood wasn't very far and easily achievable in a couple of minutes. I think it was Charles in an earlier post, calculated the distance that Haygood travelled to be about 700 feet which is a little over 2 football fields, so yeah, not very far at all. Just checkout how fast Haygood is moving in the following GIF!
It's like the Tippit shooting, Oswald had enough time to reach Tippit and they both arrived at Patton and Tenth at the same time and likewise here, Haygood had enough time to do his round and arrive back at his bike to make his call.
After rereading the entirety of the relevant posts, this entire "mystery" relies on self serving timing interpretations, Royell's initial four minute Haygood timeline to reach the top of the Triple Underpass is the obvious example of one of his exaggerations and it all goes downhill from there.

JohnM