I don't see a WaitForDSKToFinish() in the docs. Are you referring to WaitForAutoToFinish()?
The DDRs are troublesome for trying to do timed actions. My first reaction would be to make a special "play" button that would remember how long the clip is and trigger your action at the right time. Or what I would want to do is to poll the DDR at a given interval to see if the clip is approaching its last second, but the DDRs don't work with timers. So, either method doesn't work as a DDR option.
What you might be able to do is run it from the Switcher or the CG. I know the CG works with timers, but I've never tried it with the Switcher. I'm guessing that you want to perform a switcher action anyway, so that might be a place to start. Using FindModule you could ask the DDR GetPosition() and compare it to the GetLength() value. Once it gets below 1 second you could trigger the action. Accuracy would depend on how often you could poll the DDR without it bogging everything down, but it might work.
Kris