a little unrelated to @tomgross original question:
@seanupton - not sure, if that helps with subclassing: Mockup: subclassing/extending widget patterns
this way you should be able to do near-real subclassing and overload super methods. not sure, if you can call the supermethods - just used it to re-register a pattern under a different name and different trigger.
@seanupton your type-a-date pattern is a lot of code. maybe too much, related your main achievement is to have a default time value and being able to make keyboard based date/time entries. that could be an indicator that pickadate - the base pattern you extend upon - is not the right choice? also there are date parsing libraries, which can be reused.
the maintainer of pickadate points out some problems with keyboard based date/time entries and mobile devices: https://github.com/amsul/pickadate.js/issues/45 , https://github.com/amsul/pickadate.js/issues/52 . There is a related issue on mockup, suggesting to use Patternslib based date selector: https://github.com/plone/mockup/issues/617
I'm not totally in love with our datepicker and our time picker sucks a lot. 1) it has all the issues pointed out, 2) it looks like an alien. I do like the various bootstrap datepickers more. But there, a time picker is missing. I'd love to see a time picker like in android (or nokia n9, which was awesome!), based on canvas, with ui patterns like from here: http://anthonyterrien.com/demo/knob/ - still the most efficient time entry method is via a keyboard.
long story short, if a significant amount of time is going to be spent into this issue, we should also consider rewriting it completly and use something else than pickadate.