Displayed time zone field
This field is merely an option for you to indicate what time zone you want the event details to be displayed (Image 1).
Image 1
In this example, a user chooses Hawaii time as the displayed time zone as shown in Image 2. The actual time, however, is only dependent on the start and end datetime input.
Image 2
In the case above, the "Displayed time zone" field does NOT mean that the event you scheduled will be in Hawaii time. It will still show up on your calendar as your start and end datetime input. For example, per Image 3, the user's setting is in Pacific Time, and hence, the same event is still displayed in Pacific Time.

Image 3
However, when the user clicks on the event details in Google Calendar, we can see that the timing for start and end date time is adjusted to Hawaii time (Image 4).
[Image 4]
Hence, displayed time zone is merely an option for you to indicate what time zone you want the event to be displayed.
Your Workato time zone settings:
If you leave the displayed time zone field as empty, Workato will use your default Workato time zone setting instead. It can be found in User profile >>Settings. To avoid confusion, you should set their time zone setting in Workato to the same as their time zone setting in the Google Calendar.