This is one of the case where the status quo shouldn't be changed. Instead, we get treated to a rather significant dcharacter evelopment with Waku wherein he realizes how important he is to Oura-san. He doesn't even get mad for her lying or question the fact why she hid the truth from him.
Casually announcing a deadline is really an axe if anything. Heck they even introduced so much other Karins out of nowhere to boot without even getting to meet them individually. It's sad they all have these great designs but we're reduced to side characters.
Its definitely a writing strategy so authors are able to bail out when they get axed out of nowhere. At least this way, they're able to end the story neatly or transition nicely to another arc.
It's akin to 100GF's Hahari and Hakari arc.
So now... She doesn't know that he knows what she knows. And he knows that she doesn't know that he knows what she knows. The tables have turned, and we now play the next round of 5D Chess with Multiverse and Time Travel and see where this goes.