How to manually set phpMyAdmin login cookie validity time

in the config.inc.php file, which should be located in your phpadmin root folder, add this setting:

$cfg['LoginCookieValidity'] = 18000; /* in seconds */

or you can set it as below

//LoginCookieValidity
$cfg['Servers'][$i]['LoginCookieValidity'] = 18000; /* in seconds */