interval = 60000;
imgsrc = "caerdydd.jpg";

function Refresh() {
   thetime = new Date(); 

   var hour = thetime.getHours();
   if (hour >= 16 && hour < 20) {
   }
   else {
     tmp = "?" + thetime.getTime();
     var doc = document.images['llun1'].src = imgsrc + tmp;
   }
  setTimeout("Refresh()", interval);
}