Time Zone System Field

This field is used to select time zone for Platform users. Selected time zone will be used to calculate offset for date/time values before displaying them. Choose from the list of existing time zones. If no time zone is selected - time zone setting from Account info (Customer settings) will be used.

You can check "Use browser's settings to suggest time zone for new records" on field edit page. Please note that suggested time zone will have the same offset value, but it not necessarily will be actual user's time zone.