[synthetics] Add info on timezones

docs/en/observability/synthetics-command-reference.asciidoc

@@ -42,6 +42,9 @@ For example, `cat path/to/file.js | npx @elastic/synthetics --inline`.
 JSON object to pass in custom Playwright options for the agent.
 Options passed will be merged with Playwright options defined in your synthetics.config.js file. Options defined via `--playwright-options` 
 take precedence.
++
+For more details on relevant Playwright options, refer to the
+<<synthetics-configuration-playwright-options,the configuration docs>>.
 
 *`--screenshots <on|off|only-on-failure>`*::
 Captures screenshots for every step in the journey.

docs/en/observability/synthetics-configuration.asciidoc

@@ -52,17 +52,56 @@ An object that defines any variables your tests require.
 [[synthetics-configuration-playwright-options]]
 = `playwrightOptions`
 
-For available options, see the https://playwright.dev/docs/test-configuration[Playwright documentation].
+For all available options, refer to the https://playwright.dev/docs/test-configuration[Playwright documentation]. 
+
+Below are details on a few Playwright options that are particularly relevant to Elastic Synthetics including timeouts, timezones, and device emulation.
+
+[discrete]
+[[synthetics-configuration-playwright-options-timeouts]]
+== Timeouts
 
-[NOTE]
-====
 Playwright has two types of timeouts that are used in Elastic Synthetics:
 https://playwright.dev/docs/test-timeouts#action-and-navigation-timeouts[action and navigation timeouts].
 
 Elastic Synthetics uses a default action and navigation timeout of 50 seconds.
 You can override this default using https://playwright.dev/docs/api/class-testoptions#test-options-action-timeout[`actionTimeout`] and https://playwright.dev/docs/api/class-testoptions#test-options-navigation-timeout[`navigationTimeout`]
 in `playwrightOptions`.
-====
+
+[discrete]
+[[synthetics-configuration-playwright-options-timezones]]
+== Timezones and locales
+
+The Elastic global managed testing infrastructure does not currently set the timezone.
+For {private-location}s, the monitors will use the timezone of the host machine running
+the {agent}. This is not always desirable if you want to test how a web application
+behaves across different timezones. To specify what timezone to use when the monitor runs,
+you can use `playwrightOptions` on a per monitor or global basis.
+
+To use a timezone and/or locale for all monitors in the project, set
+https://playwright.dev/docs/emulation#locale%2D%2Dtimezone[`locale` and/or `timezoneId`]
+in the configuration file:
+
+[source,js]
+----
+playwrightOptions: {
+  locale: 'en-AU',
+  timezoneId: 'Australia/Brisbane',
+}
+----
+
+To use a timezone and/or locale for a _specific_ monitor, add these options to a
+journey using <<synthetics-monitor-use,`monitor.use`>>.
+
+// Uncomment note when this is added to the Synthetics Service
+
+//////
+[NOTE]
+=====
+The timezone can also be set using the {synthetics-app}.
+If you specify a timezone in the configuration file or using `monitor.use` in the journey code,
+that timezone with take precedence over the timezone set in the {synthetics-app}.
+=====
+//////
 
 [discrete]
 [[synthetics-config-device-emulation]]