JavaScript timeout timed to run specific code

<! DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 transitional//en" >
< HTML >
< head >
< title > WebForm1 </title >
< meta name = "Generator" Content = "Microsoft Visual Studio. NET 7.1" >
< meta name = "Code_language" Content = "C #" >
< meta name = "vs_defaultClientScript" content = "JavaScript" >
< meta name = "vs_targetschema" content = "http://schemas.microsoft.com/intellisense/ie5" >
< body ms_positioning = "GridLayout" >
< form ID = "Form1" method = "post" runat = "server" >
< input ID = "Txttimer" name = "Txttimer" value = "10 seconds" >
< SCRIPT LANGUAGE = "JavaScript" > ...
<!--
var waittime=300000; 10 seconds.
Timer=setinterval ("OnTimer ()", 1000);
function OnTimer () ... {
waittime=waittime-1000;
if (waittime==0) ... {
Window.opener=null;window.close ();
}
document.all ("Txttimer"). value=waittime/1000+ "seconds";
}
-->
</SCRIPT >
</form >
</Body >
</HTML >