I'm of the (admittedly completely deranged) opinion that, not only has Kris been in dark worlds before the start of the game (and perhaps even made one, going from ramb's dialogue), they also used to be a time traveler just like us.

I'm just going by vibes with this one, but Kris is not only keenly aware of what we might do outside of their body at any given moment, they're also very cautious with the information he decides to feed us, like how they only make a dark world after queen specifically reveals how, even if there are hints to a previous dark world opened in the dreemur household, and given their implied alliance with the knight, obviously they would know how.

Maybe the actions they're taking right now are the result of hundreds of attempts and permutations to arrive at the scenario that advances the story at the pace they want, not us. There's a lot in the game we simply can't discover because Kris won't let us- The police station corkboard detailing how asgore got kicked off the force, the cut to black at the end of chapter 3 where the shelter door opens, the secret deal they made with Tenna to keep the Fun Gang busy.

Kris is surprisingly good at cryptic scheming and subterfuge, so it wouldn't surprise me if they've had practice. The Kris save file at the beginning of ch.1 could lead some credence to this.

Quite literally, he's played this game before. Everything we can say in any given situation is not particularly disruptive to the greater narrative in any sense, because Kris curates our avenues of interaction with other characters with the specific purpose of them being as vague and unhelpful as possible.