cannot change default timespan of 1 hour of dataquery plugin

[duvel]

I always get values from the last hour when using the dataquery plugin. I have tried both ways described on http://pestilence.insert.gr/ to change the timespan ("select a timespan value from the cacti top graph form or by using the zoom tool (zoom in and then query)"), but I always get just data from the last hour.
Somebody knows what is the problem ?