Sorry... I said a miisleading thing.
I am thinking about create the timer and the enable button fuction in PHP to replace javascript functions into the HTML, for example.
I can see where you're coming from, but you cannot create things like timers in PHP. Since PHP is a server side language, it loads only once when the page first loads. If you would want to make a timer in PHP, you would have to somehow delay the loading of the page entirely.
You could perhaps add some sort of verification on the PHP submit if you wanted. For example, create a PHP session variable of the time before the form, then compare it to the time after the submission of the form to be sure that it is at least your timer's length between asking for both pages.
Something like this maybe:
//Before submission
$_SESSION['preSubmissionTime'] = time();
//After submission
//Captcha checks here
if((time()-$_SESSION['preSubmissionTime']) >= 5){ //Assuming your timer is 5 seconds long
//Pay the user
}else{
die('You\'re submitting too fast');
}
?>
If you're going to do something like this though, I would suggest hiding the captcha as well as the claim button with the timer. This way, the user cannot solve the captcha and press enter before the claim button has been enabled, posting the form and making themselves look like a bot/a user cheating the system. I'm not sure how the above code would work in practice, though if you can see the logic behind it you could likely add it in yourself.
