setTimeout doesn't work on iPad using Safari

We have a web app that uses setTimeout to blank out the screen after 15 minutes of non use. It's a medical application so this is an important feature.  It works fine in every browser except Safari on a mobile device (ipad, etc).

The original code was as follows:

setTimeout("WindowClose()",900000);
function Windowclose() {
     parent.main.location.href = "/cgi-bin/screensaver.cgi";
}

This works fine except on the ipad.

I scanned the Net and found this as a solution which works, but also not on the ipad.

sTimeout = setTimeout(function() {
   parent.main.location.href="/cgi-bin/screensaver.cgi";
}.bind(this),900000);

setTimeout.prototype.bind = function(parent) {
   var f = this;
   var args = [];

   for (var a = 1; a < arguments.length; a++) {
       args[args.length] = arguments[a];
   }

   var temp = function() {
      return f.apply(parent, args);
   }

   return(temp);
}


That works fine everywhere else except again on the iPad.

Does anyone have an example of some working code for the iPad or tell what's wrong with what I'm doing?