Grappster loads data every six (6) hours. Therefore your data should be (almost) always be up to date. If the data in Grappster is not correspondent to the data in Zendesk (or any other App) , it might be because Grappster didn't synchronise yet. Also note that some pointers are showing average numbers.
In the home screen you will see the overview of the current month. At the right top corner of every App overview in that screen you will find the date and time of the latest data synchronisation.