when does the cookie for login expire ?
how to change the timeout only for one visit till i close the browser ?

i tried to delete in auth_zp.php on line 45 to delete "time()+COOKIE_PESISTENCE," and also line 25 to 27 which says "time()

Did you notice COOKIE_PESISTENCE in the line you quote above? That would be the expiration time. Of course if you do not store the cookie you will not be logged in. What did you expect?

i want, that my users have each browser start to login again.
yes i noticed that, that was the reason why i deleted that, cause i read somewhere when you define there nothing it will expire when you close the browser.

i forgot to write, that i activated galleryguest user login. is this saved to the database ?

If you define nothing there, the cookie will expire with the script execution--not very useful since each page is a new script execution. If you want each browser to start with a logon, set the album_session option.

All user/passwords are saved in the database.

do you mean gallery_sessions ? - i think that only works if you have setted a password to an album and not a guestuserlogin password - i tried it - it didn't work for the galleryguestuser login

you know, in the moment, i can't set anything in my album and i don't want to, cause i want only to protect the gallery. i'ld set that in htaccess, but i'm sure zenphoto can handle this like i want it to, cause it works with the adminlogin too.

Yes, it is the Enable Gallery Sessions option (The option name in the database is album_sessions) If it is not working there is something wrong on your server with sessions. The option is entirely contained in the cookie handling so it is not possible for it to work for one kind of cookie and not for another. Besides, all the option does is prevent the cookie from being stored so that only the session is used.