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So I at last know why this plot point is so god damn screwy in the first place, and it's partly because how the game even -ATTEMPTS- to tell you this is stupid.
The reason why Rose is so hellbent at that time frame is because he's already lost control of Eternatus at that point. How do we know this? because we've had two previous events nearby the power center with large power spots and dynamaxing pokemon suddenly. These are both results of Rose already losing control of the situation, but he can't just come out and say it.
Honestly Oleana in the mine should have been more clear on answering this subject, but all they do is have her still gushing over Rose, so it's left in this dumbfuck status of "Why didn't he just wait one more day?" it also answers why this game is set up so that till you beat the game it's day cycle is locked in place. As if they knew without it the story would make even LESS logic.