Well, again, this is a matter of interpretation. Was Christ saying that only false prophets would be saying "I am he" and "The Time has Approached" so don't be misled by anyone making these statements since the true prophets would not be saying this?
Was Christ saying/implying instead that indeed, the true prophets would be saying "I am he" and "The Time has Approached" but that other false prophets would be saying the very same things so don't be misled by just anyone saying these things. In other words, make sure you're following the right prophet who would be basically declaring these same things as would other false prophets, thus don't be misled by just anyone saying these things?
If the former is the correct understanding, that only the false prophets would be declaring the "last days" then the witnesses would be false prophets for sure, since that is one of their primary themes, claiming "I am he" meaning they are God's chosen "spiritual Israel" and the "time has approached--Look out for 1874 and 1914 and 1975!" But if this is about sorting out the true prophets from the false ones who might be saying the same things generally, but with say different dates and different circumstances, then you have to go farther and compare to see if the witnesses' doctrine follows the Bible specifically or if they deviate from scripture and are false prophets.
On the other hand, the Bible clearly indicates that his chosen ones would be preaching the "good news" during the last days on an international basis before the "end" comes. So, one wonders if that "good news" would exclude any mention about the last days or the time approaching? So more than likely what Christ was saying was that many people during these times would be preaching "last days are here" type sermons just as the anointed to preach the "good news" would be, so don't be misled by this since many would be saying these things, make sure you have the right group.
Jehovah's witnesses ARE the correct group. They are the chosen ones to preach the "good news" and 1914 indeed began the "last generation" from 1914 to 1994 (80 years) which began, as prophesied with "nation vs nation, kingdom vs kingdom", the first sign, that is a WORLD WAR, whch was WWI.
Thus since lots of groups would be preaching end-times sermons and claiming to be the right religion, it was important to make sure you found the right one and not be misled by just anyone preaching this, not everyone.