In the DC area(they do this in Crystal City too) they take the credit card at the beginning so there isn't back and forth at the end. In the past they usually brought out the receipt as you said, 15-20 minutes before the end. I feel like when I went last week they did this, maybe it was closer to the end, but before credits. However I was there a few weeks ago and they waited forever, and then one of the servers/people tasked with cleaning the theater was audibly mad that people were still there, like it was our fault for the checks not being delivered. Service still sucks, waiting 15 minutes for a drink refill or popcorn is nuts.