It seems like the new PHP version in Snow Leopard wants you to explicitly set a default timezone when calculating stuff using the date() function, and will warn you about this in your script's output.
To set the date, look in /etc and find php.ini.default, open it up in your favorite editor (BBEdit work great, but sudo pico /etc/php.ini.default works as well). Look for this line:
date.timezone =
Add your preferred timezone, like so:
date.timezone = "Europe/Berlin"
Read this page in the PHP manual for supported zones and cities.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090831101932728