Isn't the ScheduleTime class doing redundant work? Why bother keeping a dictionary, dealing with ints and strings when you can directly use strftime/strptime?<p>Except for the friday/fri thing, which, to be honest, I don't see the point of. I'd rather have uniformity in my code.
While we're on the topic -- there's also <a href="http://mailchimp.com/" rel="nofollow">http://mailchimp.com/</a> if you want to outsource the job of sending subscription e-mail.