Correct me if I am incorrect, but Odine researched Ellone's ability to send one's consciousness to the past and put it all in a machine called 'Junction Machine Ellone' which Ultimecia uses to send her own consciousness back to the present and manipulate sorceress' Edea, Rinoa and Adel.
So in theory, taking into account the little I know about time travel and it's properties. Couldn't Odine destroy the Junction Machine Ellone, preventing it from getting into the hands of Ultimecia in the future, preventing her from sending her consciousness back in time, therefore making Time Compression impossible because she can't reach Ellone unless she's in the Squall's present.
Right?
While I'm on this subject, I'll bring up this scenario too. If Odine destroys Junction Machine Ellone after Edea, Rinoa and Adel have all been possessed, it would change the future and Ultimecia wouldn't be able to compress time...but that also means that Ultimecia would have never been able to send her consciousness back in time to Edea, Rinoa and Adel...so does that mean destroying Junction Machine Ellone would change the past as well as the future?
My head hurts.