Caller's Location's Timezone set on the SLA definition for incident_task table is not working:

There is no caller field existing on the Incident Task table, it is only available in the Incident table.

The system timezone is set on the Task SLA record, but the expectation would be the incident's caller's location's timezone to be set on the Task SLA record, as the Caller field has been configured on the [incident_task] table by dot walking incident.caller.

Review the 'SLATimezone' Script Include /sys_script_include.do?sys_id=e35516289f3200008f88ed93ee4bcc66 , which has the function to determine which field should be considered the Caller field:
                         

For HR records this should be the [opened_for] field, and the code sets this for the non-scoped HR tables only, not for the scoped HR tables. It will default to the [opened_by] field which could cause an incorrect timezone to be used:

                  switch (task_type) {
                  case 'incident':
                  return task.caller_id;
                  case 'incident_task':
                  return task.incident.caller_id;

Modify the above script include to include the following lines of code:

case 'incident_task':
return task.incident.caller_id;