Rails Engine providing the jquery-timepicker-addon. See trentrichardson.com/examples/timepicker/ for details.
in your js manifest (application.js):
// Jquery timepicker Addon //= require jquery-timepicker-addon
// Some (for now) very simple ujs code to initialize the timepicker (with default options) for every element with class 'datetimeselect' //= require datetimeselect.ujs.js
allow to specify options via data-attributes, and extend accordingly
maybe also provide some necessary default styles