Is this a new feature that when someone requests a book from you they place a 1 hour hold on the book before allowing the request to allow the buyer to change their mind? I've never noticed that before...

As far as I know it's always been that way.

It's always been that way - you probably just didn't notice it until now!  There is a buyers remorse when a person orders a book that is available in the system, or when a person has a book on autorequest that is posted.  You, in fact, get an automatic one hour buyers remorse when you order a book, so if you cancel within that hour, the potential sender will never know it was even requested.

If the requestor wants to opt out of the one hour delay, he can do so by sending a PM to the sender.  One more arcane PBS tidbit.

Awww...too bad.  The person who just ordered a book from me must have sent the PM before ordering.    Which explains why I couldn't find the book on hold the first time I looked through my shelf after getting the PM and did the second. :)