But ACH isn't an ungoverned system where parties get to just behave in their own best interest. It, and the timing/behaviour, are governed by the NACHA Operatin

But ACH isn't an ungoverned system where parties get to just behave in their own best interest. It, and the timing/behaviour, are governed by the NACHA Operating Rules. If you are being a bad party and failing to submit transactions on time so that you can collect a bit of extra interest, you are going to get a very large hammer brought down on you.