code: function _get_ms(a, b) {
  	debug.assert(a).is('date');
  	debug.assert(b).is('date');
  	if(a < b) {
  		return b.getTime() - a.getTime();
  	}
  	return a.getTime() - b.getTime();
  }
docs: Returns seconds between two date values
  @returns {number} Time between two values (ms)