DHTML PopUp - Cookie setzen...

[Hansilein]

// Drop-in content box- By Dynamic Drive  
// For full source code and more DHTML scripts, visit http://www.dynamicdrive.com  
// This credit MUST stay intact for use  
  
var ie=document.all  
var dom=document.getElementById  
var ns4=document.layers  
var calunits=document.layers? "" : "px"  
  
var bouncelimit=32 //(must be divisible by 8)  
var direction="up"  
  
function initbox(){  
if (!dom&&!ie&&!ns4)  
return  
crossobj=(dom)?document.getElementById("dropin").style : ie? document.all.dropin : document.dropin  
scroll_top=(ie)? truebody().scrollTop : window.pageYOffset  
crossobj.top=scroll_top-250+calunits  
crossobj.visibility=(dom||ie)? "visible" : "show"  
dropstart=setInterval("dropin()",50)  
}  
  
function dropin(){  
scroll_top=(ie)? truebody().scrollTop : window.pageYOffset  
if (parseInt(crossobj.top)<100+scroll_top)  
crossobj.top=parseInt(crossobj.top)+40+calunits  
else{  
clearInterval(dropstart)  
bouncestart=setInterval("bouncein()",50)  
}  
}  
  
function bouncein(){  
crossobj.top=parseInt(crossobj.top)-bouncelimit+calunits  
if (bouncelimit<0)  
bouncelimit+=8  
bouncelimit=bouncelimit*-1  
if (bouncelimit==0){  
clearInterval(bouncestart)  
}  
}  
  
function dismissbox(){  
if (window.bouncestart) clearInterval(bouncestart)  
crossobj.visibility="hidden"  
}  
  
function truebody(){  
return (document.compatMode && document.compatMode!="BackCompat")? document.documentElement : document.body  
}  
  
  
function get_cookie(Name) {  
var search = Name + "="  
var returnvalue = ""  
if (document.cookie.length > 0) {  
offset = document.cookie.indexOf(search)  
if (offset != -1) {  
offset += search.length  
end = document.cookie.indexOf(";", offset)  
if (end == -1)  
end = document.cookie.length;  
returnvalue=unescape(document.cookie.substring(offset, end))  
}  
}  
return returnvalue;  
}  
  
function dropornot(){  
if (get_cookie("droppedin")==""){  
window.onload=initbox  
document.cookie="droppedin=yes"  
}  
}  
dropornot()

das plugin setzt ein cookie bis zum ende der sitzung... ich will aber dass es nur 15 minuten gültig ist, wie kann ich das umschreiben? schaffs leider nicht :(

danke...