Brian,
I had a look at the code you've sent. Looks good, expect for some minor items.
1. Your inheritance path is a bit wrong, and it does not follow what I've draft on the class diagram (A task is derived from a schedule, which is not what we want).
Okay, makes sense.
2. Your setTime, setDate, set.... expect integer as parameters. We would like to submit list of integers, which is easyer to handle from a GUI perspective. Have a look at the class diagram updated by Matthew.
Actually, they expect strings. My reasoning behind that was that cron accepts ranges (e.g. 2-5), lists (e.g. 1,2,3), step values (e.g. */5) and so on. So, are we not going to have those kinds of functionality?