they need to go back regardless if its a after effect or not. it doesnt matter if this is a timed thing or if they could theoretcally be there forever. Oden needs to go back to the past and die, to set up these events, set up kinemon and co going to the future to find allies and all that.
That is the point.
Oden need to sacrifice himself for the sake of Wano in the future, to save his Scabbards and family, Kinemon and co send into the future to build up the allies. If you put Oden forever into the future as Toki did to Kinemon and co, it could have massive effects for the past.
Let say Toki has a limit to teleport multiple persons into the future, this could explain that she only can send few people in the future. In that case if she send Oden and few scabbards, Momo and co couldn´t send into the future. That could be the first problem, the next problem could be if Oden get send out of the jail Kaido would noticed it and directly attack the family of Oden, result not Scabbards their to protect Momo and co. They would be killed out if we probably count the fact that Toki can´t travel multiple people into the future.
So it make sense why Oden need to come back, he open up the way for the future where Kaido get defeat.
Like endgame, where they get the stones from the past only to use them in future and bring them back into the right time where they get the stones, so the past wouldn´t change at all. Oden has not his two swords, with meaning he couldn´t effect the future, he probably take two swords who Toki/Hiyori give him. In that case if Oden get teleport back into the future where he was in cell, his left wouldn´t effect the past.
I can see something like this in case if Oda really want Oden for the war against Kaido in the raid.