Date Locale & Time Zone settings

Locale Settings

The local settings can be found at admin/settings/date-time.

Default time zone

Sets the default time zone for the website. Think of this setting as the time zone where the organization is based. When anonymous users visit the site, time fields displayed for them will be converted to this time zone.

User-configurable time zones

Determines if individual users can set their own default time zone. When the user is logged on, this effectively overrides the above "Default time zone" setting.

First day of week:

Sets the desired first day of a week. Mostly affects calendar grid displays, but also affects date-browser output when viewing dates by week. For most US/English sites, this should be set to Sunday. Monday is also frequently used in countries that follow the ISO 8601 date standard. Also, Saturday is common among Gulf Cooperation Council countries. (see http://en.wikipedia.org/wiki/Seven-day_week#Week_number for details)

Use ISO-8601 week numbers

For USA/Canada/Australia as well as many Middle East countries, week numbers DO NOT follow the ISO-8601 standard, and this option should be unchecked (unchecked is the default behavior).
To fully comply with the ISO-8601 standard for date & time, this option should be checked & the First day of a week should be set to Monday. This is common for much of Europe & Asia.

Time Zone settings unique to each date field instance

Time zone settings can be found at: /admin/content/node-type/[machine_name_of_node-type]/fields/field_[machine_name_of_field]

Time zone handling

There are 5 different options for field Time zone handling:

1. Site's time zone - When entering data into the field, the data entered is assumed to be in the site's time zone. When the data is saved to the database, it is converted to UTC. When retrieved from the database, the data is converted to the Site's time zone for anonymous users or the User's time zone for logged in users when User-configurable time zones are enabled.
2. Date's time zone - With this option enabled, the date field adds a select box to explicitly specify the time zone for the date entered. When the date is saved to the database, it is not converted & the time zone information is saved with the date. When retrieved from the database, no conversion is performed and the date is displayed exactly as entered.
3. User's time zone - When entering data into the field, the data entered is assumed to be in the user's time zone. When the data is saved to the database, it is converted to UTC. When retrieved from the database, the data is converted to the Site's time zone for anonymous users or the User's time zone for logged in users when User-configurable time zones are enabled.
4. UTC - When entering data into the field, the data entered is assumed to be in UTC time zone. When the data is saved to the database, it is converted to UTC (e.g. no conversion necessary). When retrieved from the database, the data is converted to the Site's time zone for anonymous users or the User's time zone for logged in users when User-configurable time zones are enabled.
5. No time zone conversion - The date entered is not converted when saved to the database. When retrieved from the database, the data is NOT converted and is displayed exactly as entered.

Switch from "No time zone conversion" to "Date's time zone"

If you start off without a time zone but then realize that you need one at a later date, it's possible to switch from "No time zone conversion" to "Date's time zone" even though the UI doesn't recommend it.

Perform the switch in the field settings, but once done, execute the following query:
UPDATE content_field_foo SET field_foo_timezone = 'UTC'

...where content_field_foo is the table containing the date field data, and field_foo_timezone is the time zone column. For each field instance, this will set a proper time zone where there wasn't one before. Without doing this, your dates will show up with different times depending on the site's time zone and your users' time zones.

You may then edit the time zones to something specific other than UTC on each node's edit page.