Timetastic has a global privacy setting that means users can only see the Wallchart for their own department, they won't be able to take a look at the calendar for other departments.
You can choose your preferred privacy level in general settings:
Head to SETTINGS > GENERAL
Calendar feeds are also affected so that users will no longer have access to the 'Full Organisation' option.
Here's an example Wallchart selector of what a user can see before Department Privacy is switched on - note they can select other departments.
And this is what they see after - the ability to select another department has gone.