If you are getting the No activity within 1440 seconds; please log in again message it means that your phpMyAdmin session is set to expire in 1440 seconds by default. In order to extend phpMyAdmin timeout with a longer one, you need to change your php and phpMyAdmin configurations.

For Ubuntu 13.10/13.04/12.10/12.04:

Add/Edit /etc/phpmyadmin/config.inc.php

$cfg['LoginCookieValidity'] = 60 * 60 * 24; // 24 hours

you will need to change your php settings as well.

Add/Edit /etc/php5/apache2/php.ini

session.gc_maxlifetime = 86400 // 24 hours

Finally restart your server for changes to take effect, for this example I will assume you are using apache.

sudo service apache2 restart