This is a clever  way to add a fast DT to the Micro I timer. The idea is from Roger LaPrelle and shows his Early NOS Kiwi. He added a wire to ride in the scroll. DT will happen when the wire reaches the top of the scroll. The delay can be anything from 1/2 turn (~1.5 seconds) up to 15 seconds or so after engine cutoff. Obviously, you should not have a lot of line pull and load the timer too much. A really fast DT can save a new plane from a disastrous crash on one of the first early flights when getting the trim dialed in. A longer DT can really help when adjusting the power pattern and  transition so you do not have a long chase on a test flight.