Getting excited about going home to the Poly in Sept!

Hoping you lovely folks can help with a couple of questions.
1. Has anyone ever arrived very late, around midnight or after? What is the process?
We have a wedding we have to attend (family) on our arrival day outside of Savannah. DH is insistent he wants to drive though that night, so that puts us rolling into the Poly around midnight, or a little earlier if we're lucky. How late is the concierge desk open? Will we be able to check in that late, or should we check in online and call ahead of time to let them know we'll be late? I guess we'll miss the whole lei experience which stinks, but the kids will be zombies when we get there anyway.
2. Has anyone had success combining reservations so you don't have to switch rooms?
We chose to add a day on the end of our trip after we found out about the wedding so it's technically a different reservation. Will we have any luck combining the reservations when we check in and requesting that we remain in the same room (I should mention we rented DVC so this is not a regular resort res)? We plan to do HS that morning and return for pool time and then head out to
MNSSHP that night. We'd hate to be in between rooms during the afternoon.