Take a look at a reservation solution I built at
http://problemsets.hollyjerry.org/reserve/. Pick an
appointment to reserve, and click
Find Available Resources.
That will take you to a datetime widget I built a long time ago that lets you do all but seconds.
If you like it let me know and I'll package it up somewhat and you can have it.
I actually think that widgets such as these are most elegantly done in JavaScript: you may wish to see what freebie javascript widgets are out there.
