My first issue of Make arrived at the weekend. It's great, this issue has plans for a Kite Photography rig. I highly recommend it. The timer uses some silly putty inside a brass tube within which a long piece of dowel is inserted. An elastic band is wrapped around one end of the dowel and as the elastic band unwraps, the friction of the silly putty against the inside of the tube causes a delay before the timer activates the camera button.
Only problem being I have never seen silly putty in the UK. So I shall have to experiment with play doh or plasticene if I can't track it down.
You can but it at Amazon: