Delayed orders for armies work magnificently in many real time wargames. It’s not like it’s a new mechanic, and it’s very different to diplomatic proposals, etc. (it adds much more uncertainty and less ability to react)
Delays would make whack a mole impossible, since the enemy army won’t be there when yours arrive necessarily, thus having a defense in depth (with defensive armies in forts, etc) would be necessary to ensure safety of your borders, and wars would mostly be limited to a big stack against a big stack, and the loser have no a very hard time to recover (which is quite period appropriate for IR and CK3).
But anyway, like other I’ve always found the military aspect extremely lacking and unbelievable in Paradox games. I love that Vicky 3 is abstracting it.