AngularJS 1.2.1, HTML, CSS, JavaScript
No-Library (pure JS), HTML, CSS, JavaScript
D3 3.x, HTML, CSS, JavaScript
jQuery Compat (edge), HTML, CSS, JavaScript
I think this will be the fastest... faster than checking .getHours and .getMinutes and .getSeconds, etc.
... working together in harmony. Unfortunately the extra variable is needed. This version uses data instead of a global variable.