diff --git a/docs/item-schema.md b/docs/item-schema.md
index 8615a80..58c305e 100644
--- a/docs/item-schema.md
+++ b/docs/item-schema.md
@@ -120,7 +120,7 @@
   "use24Hour": false,
   "topOfHourAnnounce": true,
   "alarmEnabled": false,
-  "alarmTime": ""
+  "alarmTime": "12:00 AM"
 }
 ```
 
@@ -137,7 +137,8 @@
 - `use24Hour`: boolean (or `on/off` in updates), default `false`.
 - `topOfHourAnnounce`: boolean (or `on/off` in updates), default `true`.
 - `alarmEnabled`: boolean (or `on/off` in updates), default `false`.
-- `alarmTime`: blank when unset; when set, accepts `HH:MM` (24-hour mode) or `H:MM AM/PM` (12-hour mode).
+- `alarmTime`: default `12:00 AM`; accepts `HH:MM` (24-hour mode) or `H:MM AM/PM` (12-hour mode).
+- UI visibility: `alarmTime` is shown only when `alarmEnabled=true` (`visibleWhen` metadata).
 - Global defaults: `useSound=none`, `emitSound=sounds/clock.ogg`.
 - Clock speech announcement audio is emitted via `item_clock_announce` packets using `/sounds/clock/el640/*.ogg`.
 
diff --git a/docs/item-types.md b/docs/item-types.md
index f08093a..9ee5c91 100644
--- a/docs/item-types.md
+++ b/docs/item-types.md
@@ -103,7 +103,7 @@ This is behavior-focused documentation for item types and their defaults.
   - `use24Hour=false`
   - `topOfHourAnnounce=true`
   - `alarmEnabled=false`
-  - `alarmTime=""`
+  - `alarmTime="12:00 AM"`
 - Global:
   - `useSound=none`
   - `emitSound=sounds/clock.ogg`
@@ -121,6 +121,7 @@ This is behavior-focused documentation for item types and their defaults.
 - `topOfHourAnnounce`: boolean or on/off style input
 - `alarmEnabled`: boolean or on/off style input
 - `alarmTime`: `HH:MM` when `use24Hour=true`, otherwise `H:MM AM/PM`
+  - Visible only when `alarmEnabled=true` (`visibleWhen: {"alarmEnabled": true}`)
 
 ### Audio
 - Spoken clock assets live under `client/public/sounds/clock/el640/`.
diff --git a/server/app/items/types/clock/definition.py b/server/app/items/types/clock/definition.py
index a916316..3d7d727 100644
--- a/server/app/items/types/clock/definition.py
+++ b/server/app/items/types/clock/definition.py
@@ -67,7 +67,7 @@ DEFAULT_PARAMS: dict = {
     "use24Hour": False,
     "topOfHourAnnounce": True,
     "alarmEnabled": False,
-    "alarmTime": "",
+    "alarmTime": "12:00 AM",
 }
 PARAM_KEYS: tuple[str, ...] = ("timeZone", "use24Hour", "topOfHourAnnounce", "alarmEnabled", "alarmTime")
 
@@ -81,5 +81,6 @@ PROPERTY_METADATA: dict[str, dict[str, object]] = {
         "valueType": "text",
         "tooltip": "Alarm time. Uses 24-hour HH:MM when 24 hour format is on, otherwise H:MM AM/PM.",
         "maxLength": 8,
+        "visibleWhen": {"alarmEnabled": True},
     },
 }
diff --git a/server/tests/test_item_use_cooldown.py b/server/tests/test_item_use_cooldown.py
index 9db039e..d2ff7ac 100644
--- a/server/tests/test_item_use_cooldown.py
+++ b/server/tests/test_item_use_cooldown.py
@@ -286,8 +286,9 @@ async def test_clock_timezone_update_validates(monkeypatch: pytest.MonkeyPatch)
         client,
         json.dumps({"type": "item_update", "itemId": item.id, "params": {"alarmEnabled": True}}),
     )
-    assert send_payloads[-1].ok is False
-    assert "alarmtime must be a valid time" in send_payloads[-1].message.lower()
+    assert send_payloads[-1].ok is True
+    assert item.params.get("alarmEnabled") is True
+    assert item.params.get("alarmTime") == "12:00 AM"
 
     await server._handle_message(
         client,