"Trying to part Kennedy's hair prematurely (making an attempt with the limo still on Houston) would be tantamount to saying 'Here I am. Come and get me'". At that point would the jig me up? When ever the first shot rang out. Agree?
In what sense? During the firing sequence? Or ultimately? Seems Oswald didn't decide the
jig was up until the TT, by way of voicing 'that's it, it's all over now'
The JIU term means that whatever you were trying to get away with has been found out and you can no longer get away with it. Oswald's first shot did not prevent him from 'getting away with it'. Nor did his second or third shot.