notes for Woocommerce checkout fields options select:
$fields['billing']['partytime'] = array( 'label' => __('party Time', 'woocommerce'), 'placeholder' => _x('partytime', 'placeholder', 'woocommerce'), 'required' => true, 'clear' => true, 'type' => 'select', 'class' => array('css-party-time-class'), 'options' => array( '0' => __('Select Options', 'woocommerce' ), '07:00am' => __('07:00am', 'woocommerce' ), '07:15am' => __('07:15am', 'woocommerce' ), '07:30am' => __('07:30am', 'woocommerce' ), '07:45am' => __('07:45am', 'woocommerce' ), '11:00pm' => __('11:00pm', 'woocommerce' ) ) );