Releasing the information 4 days later implies it took 4 days to properly process and categorize. It probably did take some time to properly process and categorize it, because anomalous sounds happen underwater all the time, and unless it's a subsea nuclear detonation or a Russian propeller screw then it's going to go into the "figure it out later" bucket.

So what we know is it took no more then 4 days to categorize it. We don't know whether or not the system flagged it immediately, or flagged it as part of background process, or how long that took.

Joe Internet-Commentator looks at that and says "oh it was totally instant, probably".

Bill Submarine-Commander for a Hostile Power on the other hand is very interested in exactly how quick any particular detection was, to what resolution, and what implied noise-cutoffs of the network. What sort of sonic events are handled in real time vs. handled in later analysis. Because for Bill the question is "how long before I'm detected and surface ships start dropping buoys, depth charges and torpedos to kill me".