Some services will use the local date and time when you interact with them -- this is especially important when submitting GSX Repairs to Apple, as the "Received Date" (in the GSX window) is recorded in GSX as "Received Date and Time," and starts the clock on the Repair process.
To make sure your Workstation is reporting the proper Date and Time, go to Admin > Workstation Setup > Preference and select "Local Time Zone Offset." If you click on the "Information" icon, CheckIn will show you a list of geographical locations, and their Time Zone Offsets (from UTC). Enter the number that applies to your location.
Note that you may need to make an adjustment to this setting if you are currently under Daylight Savings Time (DST), and again once your location exits it.