I believe larc has it right. The story about the FDS is an illustration, nothing more. In Matt. 24:36 and Matt. 24:42 Jesus clearly states that no man will know when the Lord is coming. Then you read about the FDS in Matt. 24:45-51. Jesus then follows up with the MAIN point (no one will know the day and hour of the Lords return) in Matt. 25:13.
The WTBTS has completely twisted the verses to give them authority over others (more like the illustration of the evil slave IMHO).
THE MAIN POINT: NO MAN WILL KNOW, NOT ANGELS OF HEAVEN, NOT JESUS. ONLY THE FATHER (Matt. 24:36).
For the Society to take a small part of this chapter and start saying they know when the Lord will return is completely opposite of what Jesus was try to teach!
thinker