PHP fatal error:Pdo.php and Mysql.php (no replies)

[Mon May 06 08:05:47 2013] [error] PHP Fatal error: Maximum execution

time of 30 seconds exceeded in D:\\wwwroot\\piwik\\libs\\Zend\\Db\\Statement\\Pdo.php on line

228。
[Fri May 10 08:55:36 2013] [error] [client 192.168.132.100] PHP Fatal error: Maximum execution

time of 30 seconds exceeded in D:\\wwwroot\\piwik\\core\\Tracker\\Db\\Pdo\\Mysql.php on line

172, referer: http://www.XXX.XX.cn/.
I don't know what does the variable means ,and how to set the maximum execution.
Thank you very much!!
God bless you!!
Jocelyn