Drupal Timefield exposed filter integration (template.php)

template.php

/**
  * Preprocess output of form element
  *
  */
function yourtheme_preprocess_form_element(&$vars) {
  if (!empty($vars['element']['#id']) && ($vars['element']['#id'] == 'edit-hour')) {
    // Add special class for JS to work properly but we need to edit the #children value :/
    $children = $vars['element']['#children'];
    if (!empty($children)) {
     $vars['element']['#children'] = str_replace('form-text', 'form-text edit-timefield-timepicker filter-project-event-time', $children);
    } else $vars['#attributes']['class'][] = 'edit-timefield-timepicker';
  }
}