The Unknown or as being referred to as YMX cannot control time. Well not in the way he travels back in time, this would make no sense for the Kh storyline and leave too many holes. My theory is that he can manipulate time by manipulating memories, thus why Xemnas and Ansem SoD are appearing, and also Vanitas as well. The beings we see that resemble Xemnas, Ansem SoD and Vanitas are just nothing more than beings crafted from encounters with Sora, Riku, and Ven. I doubt this theory will hold up once the game is out. I just rewatched CoM cutscenes and I believe Nomura is going the same route as he did with Riku and Ansem SoD in that.

Valid theory cuz nomira did say that for some reason, yet to be revealed, wherever the MF appears people of darkness apear as well...im really curious to see what the real situation is....but this is very interesting

I think you might be right on your theory

Valid theory cuz nomira did say that for some reason, yet to be revealed, wherever the MF appears people of darkness apear as well...im really curious to see what the real situation is....but this is very interesting

 

Hmm maybe like this.

 

Sora's darkness = Vanitas (AND POSIBBLY XEMNAS)

Riku's darkness = Ansem SOD

I never really liked the theory of Young Master Xehanort controlling time, not the time control by itself, but the theory of he "going back in the past to fight Aqua/ Terra/Ven" as the secret enemy of BBS.

BUT! If he is the mysterious figure of BBS, than he DO CAN control time, if you fight with him you'll see that sometimes he can go back in time to avoid some damage (as far as a I remember, I just saw youtube videos, never really had a fight with him).