Calling and asking seems a good place to start.

I have no idea what the policies around these seats are but it's possible agents have discretion to assign them, so if the first agent says no you could try a few times and see if you get a different response (if one says no, hang up politely and don't push the issue). Not clear if you have elite status but that would probably increase your chances of a good outcome.

But, I don't know what the status/typical use of those particular seats is, but generally speaking other standard Delta blocked seats I know of (like the first two starboard-side EC seats on E170s, E175s, CRJ700s and CRJ900s) reliably come available at T-24, if you aren't able to convince someone to give them to you before then.