Change password protected post cookie length

Hi,
I am wondering how you change the expiry time of the cookie that stores the password for a protected post.

In wp-login.php I can see the following:

/**
	 * Filter the life span of the post password cookie.
	 *
	 * By default, the cookie expires 10 days from creation. To turn this
	 * into a session cookie, return 0.
	 *
	 * @since 3.7.0
	 *
	 * @param int $expires The expiry time, as passed to setcookie().
	 */
	$expire = apply_filters( 'post_password_expires', time() + 10 * DAY_IN_SECONDS );
	setcookie( 'wp-postpass_' . COOKIEHASH, $hasher->HashPassword( wp_unslash( $_POST['post_password'] ) ), $expire, COOKIEPATH );

	wp_safe_redirect( wp_get_referer() );
	exit();

but I do not understand how I go about changing it – I assume something I need to add to my functions.php

Thanks for any advice.