add_action( 'cmb2_init', 'yourprefix_register_about_page_metabox' );

/**
 * Hook in and add a metabox that only appears on the 'About' page
 */
function yourprefix_register_about_page_metabox() {
        // Start with an underscore to hide fields from custom fields list
        $prefix = 'rio_members';
        /**
         * Metabox to be displayed on a single page ID
         */
        $cmb_about_page = new_cmb2_box( array(
                'id'           => $prefix . 'metabox',
                'title'        => __( 'Members Signup & Expiration', 'cmb2' ),
                'object_types' => array( 'user', ), // Post type
                'context'      => 'normal',
                'priority'     => 'high',
                'show_names'   => true, // Show field names on the left

        ) );


if( current_user_can('read') ) {
    // stuff here for admins or editors


    $cmb_about_page->add_field( array(
                'name' => __( 'Members Signup & Expiration date', 'cmb2' ),
                'desc' => __( 'Set expiration date of membership', 'cmb2' ),
                'id'   => $prefix . 'datetime_expiration',
                'type' => 'text_date_timestamp',
    ) );

echo $prefix . 'datetime_expiration';

}

}