If you cannot produce a different, more plausible, and scripturally accurate meaning of Jesus' words, how can you say for sure that JW's explanation of it is wrong?
Start by reading the passages before and after that one(*). They are all about being prepared, about not knowing the day and time. Now read the "faithful servant" passage, staying mindful of that context. What is that passage about? Is it an abrupt change in topic to identify a ruler of the faithful, immediately followed by a return to the previous topic? Or is it consistent with the other passsages in Matthew 24 and 25, a warning to always be ready because you never know when the time--your time--will come?
The Watchtower interpretation only makes sense in isolation. It does not fit when the passage is read in context.
(*) Passage Topics, Matthew 24:3 through 25:46
- The Beginning of Calamities
- The Great Tribulation
- The Coming of the Son of Man
- Lesson of the Fig Tree
- Unknown Day and Hour
- As It Was in the Days of Noah
- One Taken, One Left Behind
- Hour When the Thief Comes
- Faithful or Unfaithful Servant
- Ten Virgins and Oil for Their Lamps
- Parable of the Talents
- The Judgement of Nations