Extend the authorization of the cookie expiration.

extend-auth-cookie-expiration.php

<?php

/**
 * Extend the default expiration of the authorization cookie
 *
 * @param int $time the expiration time. 14 days if $remember is true, 2 if $remember is false
 * @param int $user_id the id of the current user
 * @param bool $remember whether remember me was checked. usually false.
 *
 * @return int the new expiration
 */
function extend_auth_cookie_expiration( $time, $user_id, $remember ) {

	// If remember me was checked, return orig
	if ( $remember ){
		return $time;
	}

	// Extend from 2 days to 7 days
	return 7 * DAY_IN_SECONDS;
}

add_filter( 'auth_cookie_expiration', 'extend_auth_cookie_expiration', 10, 3 );