The time issue
I wonder...
Why did the writer/director/producer decided to put only 3 minutes on the machine, just for the sake of increasing tension for the audience?
Even some uneducated person can easily point out that most of the things Nolan did in the movie is simply impossible to be done in 2-3 minutes.
Going up to the roof of the hospital ?
Have a hide and seek game with the last appearing bad guys?
Going down to basement and got electrocuted ?