Try to do following:
1. Open file:
/usr/local/cwp/phpXX/etc/cwpsrv.conf
(replace phpXX with the php version used by your CWP)
2. Add the line:
php_admin_value[max_execution_time] = 3000
3. kill php-fpm processes:
killall php-fpm
to restart PHP-FPM and apply the new value of max_execution_time (not sure how to restart php-fpm in other way).
4.Then check the mail queue manager again.
Undo the changes and then perform the steps 2-3 to leave the default values.