Ultimecia cast Time Compression Magic + Ellone’s Power = Time Compression
I thought ultimecia casted time compression without ellone, because ellone wasn't even there at the end.

I remember, during the game. Squall talked to Ellone, Squall asked Ellone if she can bring Squall back to the past but Ellone said she can't because she doesn't know him. I dunno why though. So I assumed if she doesn't know any person then she can't send them back to the past or ellone lied.