I would strongly recommend against freely mixing languages (e.g. Perl and PHP) in a single application. If you've already got a Perl application, use it to generate the time stamps and insert them in the output (HTML) that is your form.

Some information that may be of interest in this matter:

• HTML::Template is an easy way to use template files for HTML; in this case, you could have a template variable wherever you want the timestamp/etc. to appear in your output.
• the manual pages for time, sprintf, and the POSIX module are probably useful for dealing with times and conversion. Also, a CPAN search for DateTime is informative for any complicated date math. I would keep complexity down until and unless you need it (that's always true, I think).
• A refresher on CGI::Simple is a good idea as well
• Read up on the W3C's WWW Security FAQ
• There's a section of CGI Programming with Perl titled Security that should be helpful