Like how they handle endgame, I can see something like this:
1. Oden who was waiting for his death in the cell get send into the future(probably at night where the Scabbards didn´t noticed it) 20years later.
2.Oden arrive probably at the raid day or days before(could explain why he recover), he helping the alliance to win against Kaido, would explain why Oda rush chapter 970.
3. Oden travel back into the past, in the moment where he get send into the future, like it is if he never go from his cell away, no one would noticed it, it wouldn´t have any effect for the future.
It was withe stones from endgame too, they pick up the stones from the past, change the future where Thanos get killed and go back into the past where they pick up the stones, in that case they don´t change the past who not effect the future.
Toki ability have potential to explain such stuff, Toki also already hint such thing in chapter 972.
So I wouldn´t think that is impossible to Oda to handle the event, if do it right and explain it good enough, he don´t getting problems.