Widget Dashboard Calendar

Hi there,
I`m searching for an way to expand the date period from 14 Days to minimum 3 Month. I tried it in the calendarwidget.php and changed the P14D to P3M or anything else. The Dashboard is ignoring that.
Can somebody tell me where the problem is?

Thx in Advantage

Da wäre ich auch sehr daran interessiert… Hat jemand eine Idee dazu?