First of all, I agree in general with fodder in that this suggestion mostly does not do anything that you can't already do. You can already give advanced orders as far ahead as you want, including conditional orders. You don't need the game to flip the page in the Big Book of Orders to do it for you.
This suggestion will not in any way reduce the need for checking the situation early in the turn, nor remove the advantage that a realm will have from having a "hyperactive" marshal. If you try to do any serious war planning on cruise control like this, you *will* lead your army into disaster. Yes, it might be useful for coordinating a general cross-country move, or the arrival time for a mutlti-turn move. But if you try to manage an attack three or four days ahead of time without constant checking of reports, revision of the schedule, and live confirmation of the orders, then you deserve your inevitable defeat.
But none of those really addresses my main objection to running an army with standing orders. And that's that they don't actually give you a message! I want a message in my inbox that says "attack now!" I want to know that someone laid eyeballs on the reports, assessed the situation, and decided that the situation warranted an attack. I want to be able to look back in my messages and see when an order was given, and see a history of orders. I want to know how old that standing order actually is. I want standing orders to not be 47 lines long, making me scroll through 2 screens of crap to read my messages.