The character Sean Cameron Michael played Ronald Brown was named after Dr. Emmett Brown from the 80s movie "back to the future" played by Christopher Lloyd. And his first name was named after Ronald Mallett the theoretical physicist. Who is known for his scientific position on the possibility of time travel.
The is a scene after the end of the credits which shows the news paper clipping from the letter fall to the floor which is blank. The director wanted to toy with the audience by making it blank to say are they just really crazy or will the other side reveal a story.
The calender in the Doctors office shows the correct date the 26th of October.
The film was shot in a real abandoned hospital in Cape Town called The Old Woodstock hospital.
By handing the letter to Ronald its changing history as they speak it can alter time. The line the nurse says "Did you get the letter Ronald" was said twice in the film to show things are changing. As she says it the second time we used the exact same recording of her saying it the first time.