Landis, Ready and Hickey all report that their reaction to the first shot was to look to the right and rear:
Landis - "I heard what sounded like the report of a high-powered rifle from behind me,
over my right shoulder...", "My first glance was at the President, as I was practically
looking in his direction anyway...", "I immediately returned my gaze,
over my right shoulder."
Ready - "I heard what appeared to be fire crackers going off from my position. I immediately turned to my
right rear trying to locate the source but was not able to
determine the exact location."
Hickey - "I heard what seemed to me that a firecracker exploded to the
right and rear. I stood partially up and
turned to the rear to see if I could observe anything. "
They reacted to the first shot by looking in the direction the shot came from - the right and rear of their position. This is exactly what we see in Altgens 6:

In the Z-film we see these agents until z207.
At no point do we see any of these agents turning to their right and rear.At no point do we see any of these agents reacting as they said they did. That is a fact. Any suggestions otherwise are simply not true. Ready may have changed his hand position but at no point does he make any attempt to look to his right and rear. There is not the slightest suggestion he does so. Just as there is no suggestion Landis or Hickey make such a turn.
The earliest record of these agents reacting as they said they did, is Altgens 6 (z255)
To imagine they waited for 7 seconds before turning to their right and rear is genuinely laughable.
Even to imagine they waited a full second is highly unlikely.