Wait until now to manipulate Sora and Riku? He said his first target was Riku, so why not go after him when he was still susceptible to darkness like during KH1 and CoM? Ansem SoD went back to give YMX time traveling abilites before KH1 took place considering Ansem had the brown robes when talking to YMX, so I don't get why he'd wait so long? He also could've helped Xemnas as well.

 

Of course it could be that Nomura just didn't have the plot planned that far ahead of time, but it does make you wonder.

Because you can't change the course of time. The whole future had been planned out, until near the end of KH3D. (YMX Says he already knew what would happen up to that point)

Yeah, I guess things had to go a certain way, or else things wouldn't turn out right later. Time travel dominoes--it creates quite the mindfiretruck. Watch Butterfly Effect if you don't believe me.

I still need to look at the cutscenes (I love you cyberman, starting it now!), but I think that for starters it needed to be made sure that Ansem and Xemnas were made and then defeated (well, not so sure about the defeated part...) before they could attempt anything.

I think that for starters it needed to be made sure that Ansem and Xemnas were made and then defeated (well, not so sure about the defeated part...) before they could attempt anything.

 

This is a very good point.