Setting temp cookies of 15secs

[Jawelin]

Hi. I would need to store in the client's browser a temp variable.
As asked HERE I tried different ways to do this, but never managed.

Do you know some way to set and read a cookie within a function ?

Actually I would need to know if an user, within a session, has done something. When he does it first, I could set a global/cookie var somewhere, but would know (and eventually change) that value from any php script.
And that value should expire with that user's session...

How could I do something like ?

Thanks a lot.
Bye