Detailed instructions on the solution

Create Page 0: Global Page Region and Item

Create a Region named TZ Region

Note: if you don’t want this region and item to show, set the Template to “Inline Dialog”

Create an item P0_TZ

Item Type: Text Field Warn on Unsaved Changes: Ignore

Note: if you would like this to be a Time Zone selector follow the instruction in the last section.

Create Page 0 Dynamic Action: Set Session Time Zone

Create Dynamic Action as shown:

Create True Action 1: Set Value

JavaScript Expression

Intl.DateTimeFormat().resolvedOptions().timeZone;

Create True Action 2: Execute Server-side Code

PL/SQL Code

begin
    apex_util.set_session_time_zone( P_TIME_ZONE => :P0_TZ);
end;

Create True Action 3: Execute JavaScript Code

JavaScript Code

location.reload();

Change to be a Time Zone Selector

Ensure that TZ Region and P0_TZ are visible on pages

Change P0_TZ to be a Select List

Set the List of Values to be a SQL Query

select distinct tzname d, tzname  r
       from V$TIMEZONE_NAMES
  order by 1

Duplicate the Page Load Dynamic Action and make changes to it

Change the Name to “Change Time Zone” Change the “When” settings Change the Server-side Condition Delete the “Set Value” true action