At login, the Time Zones list on the Scheduler Calendar is set to the time zone on the user's local system. By default, all time zones defined in the system appear on the list. When users select a different time zone, rendering for shifts and working hours changes accordingly, along with all associated date and time values within Service Board. To ease time zone selection, you can reduce the number of options to only those zones where your teams work. Time zone modifications are global, and affect all dispatchers.