In The Dark Knight (2008), the Joker calls into a TV show where Reese is about to reveal Batman's identity, and says that if Reese isn't dead within 60 (90?) minutes, then he [the Joker] would blow up a hospital.
I'm not even going to ask how the Joker knew Reese was on TV, but how did he get the bombs planted in the hospital so quickly and without being noticed? Were the bombs pre-planted? If so, then why? He had no idea Reese was going to go on TV. Did the Joker know that a police officer had a family member in the hospital? If so, that might make sense as he could have planned to use the "I'm going to blow up a hospital" bit for some other reason.