This will only work if you are already tuned to the same channel you want to record before you begin watching the show. As soon as you change channels, the buffer starts from zero again. You can't just tune to a channel and expect the last 30 minutes to be there in the buffer.
Please don't PM me or any other members looking for personal assistance. You'll do better by posting (after you've exhausted the search feature, of course) and taking advantage of the collective expertise of the membership instead of a single individual that may or may not be able to help you. Thank you and enjoy your stay at DDB!