codice:
function setCountDown ()
{
  seconds--;
  if (seconds < 0){
      minutes--;
      seconds = 59
  }
  if (minutes < 0){
      hours--;
      minutes = 59
  }
  if (hours < 0){
      days--;
      hours = 23
  }
  
  if(seconds == 0 && minutes == 0 && hours == 0)	location.href = "http://www.html.it/";
  
  document.getElementById("remain").innerHTML = days+" days, "+hours+" hours, "+minutes+" minutes, "+seconds+" seconds";
  setTimeout ( "setCountDown()", 1000 );
}
Non so cosa c'entra PHP, ma tant'è