i suggest you use "POV Change" than "Time Skip" as you use it in the wrong scenario but who am i to judge?

since giratina is already active in the story and is the main antagonist why not make palia and dialga reach out to him to train like some kind of time zone for dialga where the training will be because it can warp time to be slower than the real world and strenght training or dark aura training for palkia as he is related to the cosmic or space part of the pokemon universe