Here's a simple way - first, create the following Perl source code to handle the date and time function (you can actually just cut and paste):
Save the file under any name you want. For example, you may call it date.pl. Upload it to your cgi-bin using your favorite ftp program, then chmod it to 755 to make it executable.
Now to insert in into your HTML page. You will need server side includes (SSI) in order to place the output of the above code into your HTML file. Simply insert the following code fragment into your HTML file: