By default the unit is set to use UK time zone. To change this:

Enable the XWRT console in the UseMyNet settings (Only necessary for 1.9 and higher)

Visit http://10.0.0.1  (You will get the landing page, please enter valid code)

If you've not already setup a XWRT password you will be prompted to set one.

Login and go to  "System"

Here you can set the time zone.

Click on "Save Changes" then click on "Apply Changes" (You must do both for the changes to work)