cookie expire

Hi.

We'd like to change the expiration date of a Cookie when a client comes in with a certain Useragent-string.

Normally our users just get the default Cookie which expires after the session.

So I thought, nothing easier than that:

 
 when HTTP_REQUEST { 
  
 if  {([HTTP::header User-Agent] contains "LEO")} { 
 HTTP::cookie expires Cookiename_Test 18144000 
         } 
 } 
 

But this doesn't work. Actually it completely rejects the useragent. I tried different variations, by changing the Time-format, by using "persist" and all the attached options, but none did work.

Can someone tell me what is wrong with this iRule? I might just oversee something. Although the f5 isn't complaining about any syntactical issues.

thx.

Markus