How to change phpMyAdmin cookie login time?
To change phpMyAdmin's default cookie login expire time (default is 1800 sec).
Change the $cfg['LoginCookieValidity'] in file config.inc.php to set new value of time in second that you want.
Ubuntu : location of config file is /etc/phpmyadmin/config.inc.php
$cfg['LoginCookieValidity'] = 246060; // is 1 day
Remark : also change auth_type to cookie by
$cfg['Servers'][$i]['authtype'] = 'cookie'; // authtype is config , cookie , http