diff --git a/custom_components/localthings/registry/capabilities/operational.py b/custom_components/localthings/registry/capabilities/operational.py
index 27bf209..8494e6c 100644
--- a/custom_components/localthings/registry/capabilities/operational.py
+++ b/custom_components/localthings/registry/capabilities/operational.py
@@ -75,7 +75,7 @@ def _delay_hours(v):
 def _format_delay(hours):
     total_minutes = round(max(float(hours), 0) * 60)
     h, m = divmod(total_minutes, 60)
-    return f"{h}:{m:02d}:00"
+    return f"{h:02d}:{m:02d}:00"
 
 
 def _delay_field(rep):
diff --git a/tests/test_operational_capability.py b/tests/test_operational_capability.py
index 0124b3d..8411557 100644
--- a/tests/test_operational_capability.py
+++ b/tests/test_operational_capability.py
@@ -139,7 +139,7 @@ class TestDelayFieldFallback:
         assert result is not None
         path, body = result
         assert path == ["operational", "state", "vs", "0"]
-        assert body == {"x.com.samsung.da.delayEndTime": "1:30:00"}
+        assert body == {"x.com.samsung.da.delayEndTime": "01:30:00"}
 
     def test_write_targets_delay_start_time_by_default(self):
         from custom_components.localthings.registry.capabilities.operational import (
@@ -156,4 +156,4 @@ class TestDelayFieldFallback:
         result = desc.write_fn(1.5, rep)
         assert result is not None
         _path, body = result
-        assert body == {"x.com.samsung.da.delayStartTime": "1:30:00"}
+        assert body == {"x.com.samsung.da.delayStartTime": "01:30:00"}