To get the user's local time (without asking, which would be easier), you'll need to use JavaScript. And this depends entirely on whether their browser does JavaScript and whether or not they have their computer's clock set correctly. I don't know the JavaScript, but once you have the info from JavaScript, you'll need to pass it to PHP either through a URL (clicked on, enclosed in an img tag, or popped up in a new window), or through hidden form fields.
