The time period of the hospital evacuation segment is implied as being enough time to evacuate an entire hospital.  The initial moments of The Joker’s threat hitting the airwaves, Gordon is heard shouting to various police crew to evacuate Gotham General Hospital as the priority (and it happens to be the one The Joker picked).  Regardless, it’s implied that the whole ruckus about the hospital happened in less than 30 minutes since the Reese guy was about to go on a TV show to expose who Batman is (seems to imply a show teaser at the beginning of a 30 or 60 minute “news” show hosted by Gary Wallace from Weird Science).  So, it’s IMPLIED as being enough time by the dialogue of the movie but in reality it would take HOURS, if not an entire day, to completely evacuate an entire hospital.  If it was the case that there was such an evacuation ahead of time, and it was evacuated before The Joker went to Dent’s room, why was Dent not evacuated?

Why would Dent be the sole patient left (contrary to Gordon wanting desperately to keep Dent safe throughout the story)?  The implication, then, is that the hospital is being evacuated at the same time The Joker shows up to Dent’s room.  The entire exchange between The Joker and Dent took place over 2-3 minutes and when The Joker walks out of the hospital it appears to be fully evacuated.

An entire major city hospital evacuated in 3 minutes.

The realness of this movie is astounding.  Not to mention how much the building actually looked like a hospital from the outside rather than an abandoned building in the middle of an industrial zone.

In “Batman Begins”, more of an above-ground real feel was given to Gotham, but still visually well-crafted enough for an audience to feel teleported to a city where a man such as Batman would be needed and could thrive.  A place where an Arkham Asylum could be found.  A place where grimy streets could exists, mixed with the modern landscape of skyscrapers.

What we got in “The Dark Knight” was (literally) a sunny bright Chicago, and at night a glitzy glass and metallic city of commerce.  The city did not feel like Gotham.. AT ALL.  It had absolutely no character and looked like every other metropolitan city in the US.  Take the costumes and makeup (and burned faces) and gadgets away from the 3 main characters and you have the movie “Heat”.  I didn’t want to see “Heat: The Lost Batman Chapter”.  If I did, I’d want to see Al Pacino in a cape and Robert DiNero doing a trick where he makes a pencil disappear into Val Kilmer’s head.  But it’s not supposed to be “Heat”.  It’s supposed to be a BATMAN movie.  As in, a movie based on a comic book character.