diff --git a/services/core/java/com/android/server/timedetector/ServerFlags.java b/services/core/java/com/android/server/timedetector/ServerFlags.java
index 65907f1801bb3..417177fa903ef 100644
--- a/services/core/java/com/android/server/timedetector/ServerFlags.java
+++ b/services/core/java/com/android/server/timedetector/ServerFlags.java
@@ -35,6 +35,7 @@ import java.lang.annotation.Target;
 import java.time.DateTimeException;
 import java.time.Duration;
 import java.time.Instant;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
@@ -179,8 +180,13 @@ public final class ServerFlags {
     public static final @DeviceConfigKey String KEY_ENHANCED_METRICS_COLLECTION_ENABLED =
             "enhanced_metrics_collection_enabled";
 
+    /**
+     * The registered listeners and the keys to trigger on. The value is explicitly a HashSet to
+     * ensure O(1) lookup performance when working out whether a listener should trigger.
+     */
     @GuardedBy("mListeners")
-    private final ArrayMap<ConfigurationChangeListener, Set<String>> mListeners = new ArrayMap<>();
+    private final ArrayMap<ConfigurationChangeListener, HashSet<String>> mListeners =
+            new ArrayMap<>();
 
     private static final Object SLOCK = new Object();
 
@@ -207,18 +213,29 @@ public final class ServerFlags {
 
     private void handlePropertiesChanged(@NonNull DeviceConfig.Properties properties) {
         synchronized (mListeners) {
-            for (Map.Entry<ConfigurationChangeListener, Set<String>> listenerEntry
+            for (Map.Entry<ConfigurationChangeListener, HashSet<String>> listenerEntry
                     : mListeners.entrySet()) {
-                if (intersects(listenerEntry.getValue(), properties.getKeyset())) {
+                // It's unclear which set of the following two Sets is going to be larger in the
+                // average case: monitoredKeys will be a subset of the set of possible keys, but
+                // only changed keys are reported. Because we guarantee the type / lookup behavior
+                // of the monitoredKeys by making that a HashSet, that is used as the haystack Set,
+                // while the changed keys is treated as the needles Iterable. At the time of
+                // writing, properties.getKeyset() actually returns a HashSet, so iteration isn't
+                // super efficient and the use of HashSet for monitoredKeys may be redundant, but
+                // neither set will be enormous.
+                HashSet<String> monitoredKeys = listenerEntry.getValue();
+                Iterable<String> modifiedKeys = properties.getKeyset();
+                if (containsAny(monitoredKeys, modifiedKeys)) {
                     listenerEntry.getKey().onChange();
                 }
             }
         }
     }
 
-    private static boolean intersects(@NonNull Set<String> one, @NonNull Set<String> two) {
-        for (String toFind : one) {
-            if (two.contains(toFind)) {
+    private static boolean containsAny(
+            @NonNull Set<String> haystack, @NonNull Iterable<String> needles) {
+        for (String needle : needles) {
+            if (haystack.contains(needle)) {
                 return true;
             }
         }
@@ -237,8 +254,11 @@ public final class ServerFlags {
         Objects.requireNonNull(listener);
         Objects.requireNonNull(keys);
 
+        // Make a defensive copy and use a well-defined Set implementation to provide predictable
+        // performance on the lookup.
+        HashSet<String> keysCopy = new HashSet<>(keys);
         synchronized (mListeners) {
-            mListeners.put(listener, keys);
+            mListeners.put(listener, keysCopy);
         }
     }
 
diff --git a/services/core/java/com/android/server/timedetector/ServiceConfigAccessor.java b/services/core/java/com/android/server/timedetector/ServiceConfigAccessor.java
index 7f7d01c29710d..5f1400097a3a2 100644
--- a/services/core/java/com/android/server/timedetector/ServiceConfigAccessor.java
+++ b/services/core/java/com/android/server/timedetector/ServiceConfigAccessor.java
@@ -25,7 +25,6 @@ import android.annotation.Nullable;
 import android.content.Context;
 import android.os.Build;
 import android.os.SystemProperties;
-import android.util.ArraySet;
 
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
@@ -35,7 +34,6 @@ import com.android.server.timezonedetector.ConfigurationChangeListener;
 
 import java.time.Instant;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
@@ -65,11 +63,10 @@ final class ServiceConfigAccessor {
             Long.max(android.os.Environment.getRootDirectory().lastModified(), Build.TIME));
 
     /** Device config keys that affect the {@link TimeDetectorService}. */
-    private static final Set<String> SERVER_FLAGS_KEYS_TO_WATCH = Collections.unmodifiableSet(
-            new ArraySet<>(new String[] {
-                    KEY_TIME_DETECTOR_LOWER_BOUND_MILLIS_OVERRIDE,
-                    KEY_TIME_DETECTOR_ORIGIN_PRIORITIES_OVERRIDE,
-            }));
+    private static final Set<String> SERVER_FLAGS_KEYS_TO_WATCH = Set.of(
+            KEY_TIME_DETECTOR_LOWER_BOUND_MILLIS_OVERRIDE,
+            KEY_TIME_DETECTOR_ORIGIN_PRIORITIES_OVERRIDE
+    );
 
     private static final Object SLOCK = new Object();
 
diff --git a/services/core/java/com/android/server/timezonedetector/ServiceConfigAccessorImpl.java b/services/core/java/com/android/server/timezonedetector/ServiceConfigAccessorImpl.java
index b452d90b9ec79..ae52912d4821a 100644
--- a/services/core/java/com/android/server/timezonedetector/ServiceConfigAccessorImpl.java
+++ b/services/core/java/com/android/server/timezonedetector/ServiceConfigAccessorImpl.java
@@ -36,7 +36,6 @@ import android.location.LocationManager;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.provider.Settings;
-import android.util.ArraySet;
 
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
@@ -45,7 +44,6 @@ import com.android.server.timedetector.ServerFlags;
 
 import java.time.Duration;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
@@ -59,33 +57,31 @@ public final class ServiceConfigAccessorImpl implements ServiceConfigAccessor {
     /**
      * Device config keys that can affect the content of {@link ConfigurationInternal}.
      */
-    private static final Set<String> CONFIGURATION_INTERNAL_SERVER_FLAGS_KEYS_TO_WATCH =
-            Collections.unmodifiableSet(new ArraySet<>(new String[] {
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_FEATURE_SUPPORTED,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_RUN_IN_BACKGROUND_ENABLED,
-                    ServerFlags.KEY_ENHANCED_METRICS_COLLECTION_ENABLED,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_DEFAULT,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_OVERRIDE,
-                    ServerFlags.KEY_TIME_ZONE_DETECTOR_TELEPHONY_FALLBACK_SUPPORTED,
-            }));
+    private static final Set<String> CONFIGURATION_INTERNAL_SERVER_FLAGS_KEYS_TO_WATCH = Set.of(
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_FEATURE_SUPPORTED,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_RUN_IN_BACKGROUND_ENABLED,
+            ServerFlags.KEY_ENHANCED_METRICS_COLLECTION_ENABLED,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_DEFAULT,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_OVERRIDE,
+            ServerFlags.KEY_TIME_ZONE_DETECTOR_TELEPHONY_FALLBACK_SUPPORTED
+    );
 
     /**
      * Device config keys that can affect {@link
      * com.android.server.timezonedetector.location.LocationTimeZoneManagerService} behavior.
      */
-    private static final Set<String> LOCATION_TIME_ZONE_MANAGER_SERVER_FLAGS_KEYS_TO_WATCH =
-            Collections.unmodifiableSet(new ArraySet<>(new String[] {
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_FEATURE_SUPPORTED,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_RUN_IN_BACKGROUND_ENABLED,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_DEFAULT,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_OVERRIDE,
-                    ServerFlags.KEY_PRIMARY_LTZP_MODE_OVERRIDE,
-                    ServerFlags.KEY_SECONDARY_LTZP_MODE_OVERRIDE,
-                    ServerFlags.KEY_LTZP_INITIALIZATION_TIMEOUT_MILLIS,
-                    ServerFlags.KEY_LTZP_INITIALIZATION_TIMEOUT_FUZZ_MILLIS,
-                    ServerFlags.KEY_LTZP_EVENT_FILTERING_AGE_THRESHOLD_MILLIS,
-                    ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_UNCERTAINTY_DELAY_MILLIS
-            }));
+    private static final Set<String> LOCATION_TIME_ZONE_MANAGER_SERVER_FLAGS_KEYS_TO_WATCH = Set.of(
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_FEATURE_SUPPORTED,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_RUN_IN_BACKGROUND_ENABLED,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_DEFAULT,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_SETTING_ENABLED_OVERRIDE,
+            ServerFlags.KEY_PRIMARY_LTZP_MODE_OVERRIDE,
+            ServerFlags.KEY_SECONDARY_LTZP_MODE_OVERRIDE,
+            ServerFlags.KEY_LTZP_INITIALIZATION_TIMEOUT_MILLIS,
+            ServerFlags.KEY_LTZP_INITIALIZATION_TIMEOUT_FUZZ_MILLIS,
+            ServerFlags.KEY_LTZP_EVENT_FILTERING_AGE_THRESHOLD_MILLIS,
+            ServerFlags.KEY_LOCATION_TIME_ZONE_DETECTION_UNCERTAINTY_DELAY_MILLIS
+    );
 
     private static final Duration DEFAULT_LTZP_INITIALIZATION_TIMEOUT = Duration.ofMinutes(5);
     private static final Duration DEFAULT_LTZP_INITIALIZATION_TIMEOUT_FUZZ = Duration.ofMinutes(1);