I know that Starwood (before being purchased by Marriott) would not provide night credit if you didn't stay over night. The OP's situation would result in a "stay" credit, but not a "night" credit. Not sure if they have or will change their rules now that Marriott has purchased them.

But with that said, in the hypothetical "arriving after midnight" scenario, the person did stay overnight and thus should, and normally automatically will get, a night credit. In the OP's specific situation, they didn't stay overnight. So technically they shouldn't get a night credit.

But as shown, it looks like customer service was willing to modify the the check-out date to give the OP that night credit (even though they probably didn't have to do that). ^