Endwalker was a great mess(SPOILERS)

[lezard21]

The best way to understand this time travel is basically:

Time travel isn't real, there is nothing to understand. They can make up whatever rule they want, like you can only travel back in time to any Tuesday where a Loporrit used a green hat but not any other day. The thing is the bare minimum you have to do if you want to use a lazy plot advancing tool like time travel is to stay consistent to those rules you yourself established.

In ShB we have cat husband traveling back in time to avert the apocalypse. He stays in the past for 100 years and never once mentions the fact about going back to his time or being on a timer to fulfill his mission. After he succeeds he does mention that he is surprised he didn't poof into non existance and arrives to the conclusion that they created a separate timeline, while his own post apocaliptic timeline still exists somewhere.

Then in EW time travel is suddenly a 2-way rotating door but you can't remain in the past for too long and also also you can't change the past to create a separate timeline where the world didn't explode because uuuh..."hey mark, why are we using time travel in the plot again??" "Idk we needed an excuse to shoehorn more Emet Selch into the plot because twitter made a lot of yaoi with him".

Emet would involve Hermes and then Hermes would have a chance to remember the events that happened. Remember what she said, Hermes is needed to deal with the incoming calamities, not only the calamity of the Final Days. She couldn't risk the problem of Hermes betraying the Ancients at that point in time before the Final Days happen, nor can the convocation capture and require Hermes to reveal everything he knows about Dynamis

Why not? The reason why the Echo doesn't solve all the WoL problems is because the WoL can't control it and happens at random, but Venat was shown to be able to use it at will. Surely they have other mind probing methods in the past. Not to mention that Hermes' involvement in the resolution of the Final Days can only happen if the Final Days actually happen, an event that does not happen immediately after Meteion leaves Planetos. If Venat warns them early on, even if Hermes decides not to cooperate they can preemptively do something about the whole thing. Hermes resolution happens as a last ditch effort after half the planet had already been destroyed.

And finally, Venat knows what solution Hermes proposes (ie. summon Zodiark to sugar coat the planet in aether) so he really isn't needed.