First, is this conventional corn?  or RR corn?  or LL corn?  or??

I'd try to delay that second application of Roundup as long as I could, to give that grass more time to leaf out.

I'd go ahead and put your anhydous down, and then plant the corn.  Wait about 6-7 days.  Watch the corn. Dig some up to see how fast it is germinating.  When it has its roots started, and just starting to put out its shoot, that is when I would make the second application of Roundup, with the 2,4-D.   Time to time this so it is about 1-2 days before the corn is ready to spike.

If it is RR corn, and you would rather do it, you could let the corn spike thru, and then use Roundup + Dicamba instead of 2,4-D.....  understanding the risks of using Dicamba and drift onto neighbor's crops, and how to make sure it doesn't drift.