In reality, "The Story of an Hour" does observe the Aristotelian unities of time, action, and place that comprise the structure of a short story. Particularly, "The Story of an Hour" is true to the unity of time, which dictates that the events in a short story should fit within the time frame of one day, or less.
Unities aside, it is true that the story carries much more "punch" when the powerful, life-changing events that take place happen to occur in such a short period of time.
The news of the death of Brently Mallard comes a shock to his young wife, and her entire view of life instantly shifts. In fact, the switch from grieving widow to happy, newly-liberated woman is so quick that her feelings of freedom lasts longer than any tears she may have shed at the beginning.
This quickness in action is juxtaposed to the fact that the marriage of Louise and Brently Mallard, regardless of how long it lasted, seems to have dragged on for much longer than Mrs. Louise would have wanted. Hence, it comes to no surprise that her desperation to be freed from the rigors of marriage helps move the story forward quicker onto what would be the potential, second half of her life. In other words, had she not been Louise Mallard, and instead a typical female of her generation, we would have had to witness the entire grieving process of the woman.
There would be no one to live for during those coming years; she would live for herself. There would be no powerful will bending hers in that blind persistence with which men and women believe they have a right to impose a private will upon a fellow-creature.
,,,,,,,"Free! Body and soul free!"
All this shows that Ms. Mallard wasted no time, whether she did it purposely or instinctively to, literally, shed away the death of her husband and find solace in a new life of freedom. All of her pain during marriage is also narrated quite quickly and on point. We aren't told much of her history, just the fact that the woman is happy now that the man is dead.
As we move on to what happens next, in comes Brently Mallard, fresh from work, and opens the door. The shock of seeing the man that was presumably dead sends his wife into yet another shock that kills her. Yes, this chain of events may very well happen in a period of an hour or less. Just imagine yourself with a heart condition, which Louise had one, and having two major events hit you back to back. Anyone would have gone through the same process, or at least a similar one.
Therefore, we would lose a lot of poignancy had this short series of events been stretched out into chapters and turned into a novel. While more details could be included in a novel, it would never read with the same level of intensity and surprise as a short story would. After all, don't we all essentially pick "the short story format" when we want to retell something to really shock and impress others? This is one of those examples where less is definitely more.