But if you are using Plesk, change your settings in :
/usr/local/psa/admin/htdocs/domains/databases/phpMyAdmin/libraries/config.default.php
Change $cfg['ExecTimeLimit'] = 300; to $cfg['ExecTimeLimit'] = 0;
And restart with Plesk UI or use:
/etc/init.d/psa restart
and
/etc/init.d/httpd restart