diff --git a/tests/phpunit/tests/date/currentTime.php b/tests/phpunit/tests/date/currentTime.php
index c98292ef0d..72d50abfba 100644
--- a/tests/phpunit/tests/date/currentTime.php
+++ b/tests/phpunit/tests/date/currentTime.php
@@ -7,6 +7,17 @@
  */
 class Tests_Date_CurrentTime extends WP_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset changed options to their default value.
+		update_option( 'gmt_offset', 0 );
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * @ticket 34378
 	 */
diff --git a/tests/phpunit/tests/date/dateI18n.php b/tests/phpunit/tests/date/dateI18n.php
index 9279aca4eb..5bd340b91d 100644
--- a/tests/phpunit/tests/date/dateI18n.php
+++ b/tests/phpunit/tests/date/dateI18n.php
@@ -7,6 +7,17 @@
  */
 class Tests_Date_DateI18n extends WP_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset changed options to their default value.
+		update_option( 'gmt_offset', 0 );
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * @ticket 28636
 	 */
diff --git a/tests/phpunit/tests/date/getFeedBuildDate.php b/tests/phpunit/tests/date/getFeedBuildDate.php
index c1d9edb66c..5f0416ce53 100644
--- a/tests/phpunit/tests/date/getFeedBuildDate.php
+++ b/tests/phpunit/tests/date/getFeedBuildDate.php
@@ -11,7 +11,7 @@ class Tests_Date_GetFeedBuildDate extends WP_UnitTestCase {
 	public function tear_down() {
 		global $wp_query;
 
-		update_option( 'timezone_string', 'UTC' );
+		update_option( 'timezone_string', '' );
 
 		unset( $wp_query );
 
diff --git a/tests/phpunit/tests/date/getPermalink.php b/tests/phpunit/tests/date/getPermalink.php
index 41977c7734..195717dbd8 100644
--- a/tests/phpunit/tests/date/getPermalink.php
+++ b/tests/phpunit/tests/date/getPermalink.php
@@ -10,7 +10,7 @@ class Tests_Date_GetPermalink extends WP_UnitTestCase {
 
 	public function tear_down() {
 		delete_option( 'permalink_structure' );
-		update_option( 'timezone_string', 'UTC' );
+		update_option( 'timezone_string', '' );
 		// phpcs:ignore WordPress.DateTime.RestrictedFunctions.timezone_change_date_default_timezone_set
 		date_default_timezone_set( 'UTC' );
 
diff --git a/tests/phpunit/tests/date/getPostTime.php b/tests/phpunit/tests/date/getPostTime.php
index ad9eb0cf31..21b9c8675b 100644
--- a/tests/phpunit/tests/date/getPostTime.php
+++ b/tests/phpunit/tests/date/getPostTime.php
@@ -9,6 +9,16 @@
  */
 class Tests_Date_GetPostTime extends WP_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset the timezone option to the default value.
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * @ticket 28310
 	 */
diff --git a/tests/phpunit/tests/date/mysql2date.php b/tests/phpunit/tests/date/mysql2date.php
index 7c83446b00..b53a57cfac 100644
--- a/tests/phpunit/tests/date/mysql2date.php
+++ b/tests/phpunit/tests/date/mysql2date.php
@@ -11,6 +11,9 @@ class Tests_Date_mysql2date extends WP_UnitTestCase {
 		// phpcs:ignore WordPress.DateTime.RestrictedFunctions.timezone_change_date_default_timezone_set
 		date_default_timezone_set( 'UTC' );
 
+		// Reset the timezone option to the default value.
+		update_option( 'timezone_string', '' );
+
 		parent::tear_down();
 	}
 
diff --git a/tests/phpunit/tests/date/query.php b/tests/phpunit/tests/date/query.php
index e3f4ba0f6f..7e3cd73392 100644
--- a/tests/phpunit/tests/date/query.php
+++ b/tests/phpunit/tests/date/query.php
@@ -21,6 +21,16 @@ class Tests_Date_Query extends WP_UnitTestCase {
 		$this->q = new WP_Date_Query( array( 'm' => 2 ) );
 	}
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset the timezone option to the default value.
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	public function test_construct_date_query_empty() {
 		$q = new WP_Date_Query( array() );
 		$this->assertSame( 'AND', $q->relation );
diff --git a/tests/phpunit/tests/date/wpTimezone.php b/tests/phpunit/tests/date/wpTimezone.php
index 8b1f09e4d1..3b60462163 100644
--- a/tests/phpunit/tests/date/wpTimezone.php
+++ b/tests/phpunit/tests/date/wpTimezone.php
@@ -8,6 +8,17 @@
  */
 class Tests_Date_wpTimezone extends WP_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset changed options to their default value.
+		update_option( 'gmt_offset', 0 );
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * @ticket 24730
 	 *
diff --git a/tests/phpunit/tests/date/xmlrpc.php b/tests/phpunit/tests/date/xmlrpc.php
index 6344265e1f..26285aa403 100644
--- a/tests/phpunit/tests/date/xmlrpc.php
+++ b/tests/phpunit/tests/date/xmlrpc.php
@@ -8,6 +8,16 @@
  */
 class Tests_Date_XMLRPC extends WP_XMLRPC_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset the timezone option to the default value.
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * @ticket 30429
 	 *
diff --git a/tests/phpunit/tests/formatting/date.php b/tests/phpunit/tests/formatting/date.php
index 32e68d8f1a..c08a94710c 100644
--- a/tests/phpunit/tests/formatting/date.php
+++ b/tests/phpunit/tests/formatting/date.php
@@ -6,6 +6,17 @@
  */
 class Tests_Formatting_Date extends WP_UnitTestCase {
 
+	/**
+	 * Cleans up.
+	 */
+	public function tear_down() {
+		// Reset changed options to their default value.
+		update_option( 'gmt_offset', 0 );
+		update_option( 'timezone_string', '' );
+
+		parent::tear_down();
+	}
+
 	/**
 	 * Unpatched, this test passes only when Europe/London is not observing DST.
 	 *