Cycle times not being used

I have a custom python script that is being run by zencommand every 300 seconds, it replaces ping in some hosts that are over a slow line (to minimize traffic)

It's a homemade script that checks for icmp connectivty after a certain time, (depends on several conditions).
At the end, I finnish the script returning one of the classical nagios values (2 when ther is an error)

    if estat == "OK":
print "Exit 0 OK | Up=2\n"
sys.exit(0)
elif estat == "CRIT":
print "Exit 2 CRIT | Up=0\n"
sys.exit(2)

The problem is that the event is not updated every 300 seconds as I would expect, to fix the wrong state, I use one of these ways:

- Close the event and wait for an automated recheck

- Call the event from the zenoss server with "zencommand run -v 10 --device=devicename --showfullcommand"