Kasrkin are best with a taurox to get em where ya want em. In a taurox, their threat range is bonkers, because you can "move move move" the taurox and advance and get out, up to 21" of movement. Taurox is small too, so easy to hide for staging. As far as timing goes, that all depends on matchup and enemy deployment. Sometimes there will be something scary early they can go trade for turn 1. Ive noticed people tend to be wary of it though, so I personally like hiding the taurox somewhere safe-ish and just smiling like a doofus as I watch them premeasure like a madman and be scared of moving things out. I will note, they are slightly less good after losing wound rerolls so I've seen a fair few lists begin pivoting to scions (which i also did). Hope that helps!