What's the algorithm to initiate the shutdown procedure prescribed in the Scheduler Module? It never seems to run. Usually a job will abort for some reason, but then the mount continues to track all the way until morning with the dust cap open. When is Ekos supposed to do the shutdown? I have the preemptive shutdown set to two hours. Can I just have a failsafe shutdown script run at a scheduled time (like dawn?).

Right, you need to enable the preemptive shutdown. Typically, in combination with the twilight setting, the scheduler executes the shutdown actions that are ticked.