That matches my experience using them as well. I always turn them in when I check-in. Now if I'm staying at a hotel on a BB rate, the hotel staff usually won't give me the BB until check-out time.

That's dependent on the hotel. Many offer them at check-in, because there's a bit of paperwork. Some want to do it at check-out - for those, I usually ask for them at check-in, explaining that I plan to do an expedited check-out in the AM, and don't want to have to wait on line and/or for them to do it later.