I wouldn't take a risk hoping for check in that early. It might not pay off then you'll be stuck out and about when you really wanted some rest before the wedding.

I would book a day room either direct with a hotel or via the link above, and, book the same type of room in the same hotel for that evening/the rest of your stay.

If you book via separate sites then track down an email address that goes to the hotel, and let them know you are the same people so they can allocate one room to you without you having to switch later in the day.