How quickly they process the information, how accuratly they could determine the source, and how accuratly they could determine the location would all be fairly sensitive information.
Basically what I’m saying is that if they announced right after it happened that “Hey guys that sub imploded at X depth and the debris field will be at Y location because we heard a pressure vessel of the correct size crush followed by the sound of something of roughly the correct mass crashing into the sea floor.” Then everyone would know how capable our equipment is.
Basically announcing it days later gives a conclusion to the questions of what happened and also will likely keep others from meeting a similar fate. Not to mention the benefit of telling other countries that “Yes we can and will find out about what goes on underwater, just how quickly is more of a mystery… For you.”