The devices must remain in GMT time to function correctly. All the events are logged in the DB as GMT so they are displayed correctly to the users as well as other fuctions on the backend. If the user would like the SIEM to be in local time you can change how the GUI displays but the backend must remain in GMT.
To change the GUI:
1. Log in as your user
2. At the top right corner select "options"
3. Select the Time Zone of your local time
With the above change all your alerts will now be displayed in your local time.