Obviously too late now for the OP (who has been and gone), but...:

Although Timmendorf is a pleasant enough place it's not somewhere I would go out of my way to visit. It's just a beach resort like many others, and the town itself is pretty boring. Travemünde is closer, and has more to offer... the river estuary with its harbour, the Priwall peninsula, the S/S Passat, the Brodten Cliffs.

If I had time to spare in Lübeck, and I wanted to do two out-of-town excursions, I'd choose Ratzeburg as the other one - a pretty little lakeside town about an hour south.