diff --git a/lib/logitech_receiver/settings_templates.py b/lib/logitech_receiver/settings_templates.py
index 0104d4b1..f18aae7c 100644
--- a/lib/logitech_receiver/settings_templates.py
+++ b/lib/logitech_receiver/settings_templates.py
@@ -1749,18 +1749,56 @@ class HeadsetMixBalance(settings.Setting):
     validator_options = {"byte_count": 1}
 
 
+class _AutoSleepRangeValidator(settings_validator.RangeValidator):
+    """Single-slot read-modify-write validator for HID++ 0x0108 AutoSleep.
+
+    0x0108 is not a single timer: V3 has two uint8 bytes, V4+ has three. Each
+    byte is an independent timer slot. Solaar exposes only the user-facing slot
+    today and preserves the others via RMW; writing zero into the other slots
+    causes the firmware to reject the request.
+
+    Wire byte layout per feature version:
+      V<3: [timer]
+      V3:  [reserved, timer]            — preserve byte[0]
+      V4+: [timer_a, timer_b, timer_c]  — preserve byte[1], byte[2]
+    """
+
+    def __init__(self, byte_count, **kwargs):
+        super().__init__(byte_count=byte_count, **kwargs)
+        # V3 sources the user-controllable timer from byte[1] per LGHUB.
+        self._slot = 1 if byte_count == 2 else 0
+
+    def validate_read(self, reply_bytes):
+        if len(reply_bytes) <= self._slot:
+            raise AssertionError(
+                f"{self.__class__.__name__}: read returned {len(reply_bytes)} bytes, expected ≥ {self._slot + 1}"
+            )
+        return reply_bytes[self._slot]
+
+    def prepare_write(self, new_value, current_value=None):
+        if new_value < self.min_value or new_value > self.max_value:
+            raise ValueError(f"invalid choice {new_value!r}")
+        if current_value is None:
+            payload = bytearray(self._byte_count)
+        else:
+            payload = bytearray(current_value[: self._byte_count])
+            if len(payload) < self._byte_count:
+                payload.extend(b"\x00" * (self._byte_count - len(payload)))
+        if payload[self._slot] == new_value:
+            return None
+        payload[self._slot] = new_value
+        return bytes(payload)
+
+
 class HeadsetAutoSleep(settings.Setting):
     name = "headset-auto-sleep"
     label = _("Auto Sleep Timeout")
-    description = _("Idle time in minutes before the headset enters sleep mode (0 = disabled).")
+    description = _("Headset idle-timer slot (0 = disabled). Units are device-specific.")
     feature = _F.CENTURION_AUTO_SLEEP
     rw_options = {"read_fnid": 0x00, "write_fnid": 0x10}
-    validator_class = settings_validator.RangeValidator
+    validator_class = _AutoSleepRangeValidator
     min_value = 0
-    # Wire format byte count depends on feature version (V<3: 1B, V=3: 2B, V>=4: 3B).
-    # UI slider is capped at 240 min regardless — firmware accepts larger values, but
-    # a 31-year slider (24-bit max) is not useful.
-    max_value = 240
+    max_value = 255  # uint8 slot
     validator_options = {"byte_count": 1}
 
     @classmethod
@@ -1773,7 +1811,7 @@ class HeadsetAutoSleep(settings.Setting):
         else:
             byte_count = 1
         rw = settings.FeatureRW(cls.feature, **cls.rw_options)
-        validator = settings_validator.RangeValidator(min_value=0, max_value=cls.max_value, byte_count=byte_count)
+        validator = _AutoSleepRangeValidator(min_value=0, max_value=cls.max_value, byte_count=byte_count)
         return cls(device, rw, validator)