if you're getting "white screened", it's usually because the PHP encountered a problem whilst executing, and you don't have error reporting on. Check your error log.
Useful function to retrieve difference in times
The best PHP resource
A good PHP FAQ
PLEASE remember to wrap your code in [PHP] tags.
// Replace this
// With this
// Then check for values/forms. Some IE versions don't send the submit button
Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.