everything i've read indicates you just have to wait until someone accepts the request.  then you click the 'i cannot mail' button, and the requestor goes right back to first on the WL.

i wouldn't worry about whether the request times out or not for the first person (or more).   there's nothing you can do about people who don't check in often enough to accept any WL books offered to them, and possibly they're inactive and then you're just weeding them out for the next person to post a copy.

You should be able to PM the person it's on hold for.  There should be a PM link on that request.  I'd PM the person and let them know the situation and ask them to accept the book so that you can cancel (which'll return them to their #1 position on the WL) and keep the book from rolling over from person to person.

I had this same situation happen to me.  I posted a WL book and accidentally got it wet while it was pending.  I PM'd the person and told them to accept and I'd have to cancel.  Luckily the 1st person responded and I didn't have to wait through any time outs.  To keep their place in line, they have to accept and you have to cancel. If they decline the book, they'll have to go back to the end of the line.