The launch has no delay window in it. If it doesn’t happen at the right moment, then you have to scrub for the backup date and time.
Based on the speed of the ISS and the amount of fuel and payload of the supply rocket, you have to launch at a certain time or you’ll miss the ISS.
Like a quarterback throwing a pass to a crossing receiver on a timing route. The receiver has to be on his spot at an exact moment, because the quarterback is throwing to the spot, not to the man. If the receiver is held, the pass will be incomplete.
Tweeeeet...."Defensive pass interference! 15,000 mile penalty...still 1st down!"
Ah!
Got it.