Item update internal larger then 1 day

[boneyard]

I would like to poll the value of an item only once a week, when converting this to seconds and trying to enter it i get this error: "Warning. Incorrect value for field "Update interval (in sec)": must be between 0 and 86400."

(how) can i configure an Update interval larger then 1 day?

[edit] Zabbix 2.0.6