You would not have wanted to look at any earlier point like you were about to invade Osirion.  Keltham might not have liked that, and you wouldn't have had those definitely-not-hostages yet.

So you would not be ready to invade immediately after the deadline passed, because you couldn't visibly prepare before that.

But once that deadline had passed, you would start carrying out Cheliax's previous plan, to, then begin readying its forces to invade Osirion.

You would not have wanted to look at any earlier point like you were about to invade Osirion.  Keltham might not have liked that, and you wouldn't have had those definitely-not-hostages yet.

So you would not be ready to invade immediately after the deadline passed, because you couldn't visibly prepare before that.

But once that deadline had passed, you would start carrying out Cheliax's previous plan, to then begin readying its forces to invade Osirion.