diff --git a/homeassistant/components/duco/sensor.py b/homeassistant/components/duco/sensor.py
index 2c157d473e00..5899f7d677fd 100644
--- a/homeassistant/components/duco/sensor.py
+++ b/homeassistant/components/duco/sensor.py
@@ -34,6 +34,12 @@ _LOGGER = logging.getLogger(__name__)
 
 PARALLEL_UPDATES = 0
 
+_CONTINUOUS_VENTILATION_STATES = {
+    VentilationState.CNT1,
+    VentilationState.CNT2,
+    VentilationState.CNT3,
+}
+
 
 @dataclass(frozen=True, kw_only=True)
 class DucoSensorEntityDescription(SensorEntityDescription):
@@ -85,7 +91,9 @@ SENSOR_DESCRIPTIONS: tuple[DucoSensorEntityDescription, ...] = (
         device_class=SensorDeviceClass.TIMESTAMP,
         value_fn=lambda node: (
             dt_util.utc_from_timestamp(node.ventilation.time_state_end)
-            if node.ventilation and node.ventilation.time_state_end != 0
+            if node.ventilation
+            and node.ventilation.state not in _CONTINUOUS_VENTILATION_STATES
+            and node.ventilation.time_state_end != 0
             else None
         ),
         node_types=VENTILATION_CAPABLE_NODE_TYPES,
diff --git a/tests/components/duco/test_sensor.py b/tests/components/duco/test_sensor.py
index 9cf809fc9878..b7ce79b1fd5a 100644
--- a/tests/components/duco/test_sensor.py
+++ b/tests/components/duco/test_sensor.py
@@ -95,11 +95,22 @@ async def test_ventilation_related_sensors_created_for_supported_node_types(
     assert hass.states.get("sensor.office_co2_state_end_time") is None
 
 
+@pytest.mark.parametrize(
+    ("ventilation_state", "expected_state_end"),
+    [
+        pytest.param(VentilationState.MAN1, "2023-11-14T22:20:59+00:00", id="timed"),
+        pytest.param(VentilationState.CNT1, STATE_UNKNOWN, id="continuous-1"),
+        pytest.param(VentilationState.CNT2, STATE_UNKNOWN, id="continuous-2"),
+        pytest.param(VentilationState.CNT3, STATE_UNKNOWN, id="continuous-3"),
+    ],
+)
 async def test_ventilation_related_sensors_created_for_box_node(
     hass: HomeAssistant,
     mock_config_entry: MockConfigEntry,
     mock_duco_client: AsyncMock,
     mock_sensor_nodes: list[Node],
+    ventilation_state: VentilationState,
+    expected_state_end: str,
 ) -> None:
     """Test ventilation-related sensors are created for the box node.
 
@@ -111,6 +122,7 @@ async def test_ventilation_related_sensors_created_for_box_node(
         mock_sensor_nodes[0],
         ventilation=replace(
             mock_sensor_nodes[0].ventilation,
+            state=ventilation_state,
             flow_lvl_tgt=42,
             time_state_end=1700000459,
         ),
@@ -124,7 +136,7 @@ async def test_ventilation_related_sensors_created_for_box_node(
 
     state = hass.states.get("sensor.living_ventilation_state")
     assert state is not None
-    assert state.state == "auto"
+    assert state.state == ventilation_state.lower()
 
     state = hass.states.get("sensor.living_target_flow_level")
     assert state is not None
@@ -132,7 +144,7 @@ async def test_ventilation_related_sensors_created_for_box_node(
 
     state = hass.states.get("sensor.living_state_end_time")
     assert state is not None
-    assert state.state == "2023-11-14T22:20:59+00:00"
+    assert state.state == expected_state_end
 
     assert hass.states.get("sensor.office_co2_ventilation_state") is None
     assert hass.states.get("sensor.office_co2_target_flow_level") is None