diff --git a/homeassistant/helpers/condition.py b/homeassistant/helpers/condition.py
index 4785612f114..e4335e2f2e4 100644
--- a/homeassistant/helpers/condition.py
+++ b/homeassistant/helpers/condition.py
@@ -225,15 +225,27 @@ def template_from_config(config, config_validation=True):
 
 
 def time(before=None, after=None, weekday=None):
-    """Test if local time condition matches."""
+    """Test if local time condition matches.
+
+    Handle the fact that time is continuous and we may be testing for
+    a period that crosses midnight. In that case it is easier to test
+    for the opposite. "(23:59 <= now < 00:01)" would be the same as
+    "not (00:01 <= now < 23:59)".
+    """
     now = dt_util.now()
     now_time = now.time()
 
-    if before is not None and now_time > before:
-        return False
+    if after is None:
+        after = dt_util.dt.time(0)
+    if before is None:
+        before = dt_util.dt.time(23, 59, 59, 999999)
 
-    if after is not None and now_time < after:
-        return False
+    if after < before:
+        if not after <= now_time < before:
+            return False
+    else:
+        if before <= now_time < after:
+            return False
 
     if weekday is not None:
         now_weekday = WEEKDAYS[now.weekday()]
diff --git a/tests/helpers/test_condition.py b/tests/helpers/test_condition.py
index 8eaee797e73..e1813f6ba1c 100644
--- a/tests/helpers/test_condition.py
+++ b/tests/helpers/test_condition.py
@@ -1,5 +1,8 @@
 """Test the condition helper."""
+from unittest.mock import patch
+
 from homeassistant.helpers import condition
+from homeassistant.util import dt
 
 from tests.common import get_test_home_assistant
 
@@ -66,3 +69,28 @@ class TestConditionHelper:
 
         self.hass.states.set('sensor.temperature', 100)
         assert test(self.hass)
+
+    def test_time_window(self):
+        """Test time condition windows."""
+        sixam = dt.parse_time("06:00:00")
+        sixpm = dt.parse_time("18:00:00")
+
+        with patch('homeassistant.helpers.condition.dt_util.now',
+                   return_value=dt.now().replace(hour=3)):
+            assert not condition.time(after=sixam, before=sixpm)
+            assert condition.time(after=sixpm, before=sixam)
+
+        with patch('homeassistant.helpers.condition.dt_util.now',
+                   return_value=dt.now().replace(hour=9)):
+            assert condition.time(after=sixam, before=sixpm)
+            assert not condition.time(after=sixpm, before=sixam)
+
+        with patch('homeassistant.helpers.condition.dt_util.now',
+                   return_value=dt.now().replace(hour=15)):
+            assert condition.time(after=sixam, before=sixpm)
+            assert not condition.time(after=sixpm, before=sixam)
+
+        with patch('homeassistant.helpers.condition.dt_util.now',
+                   return_value=dt.now().replace(hour=21)):
+            assert not condition.time(after=sixam, before=sixpm)
+            assert condition.time(after=sixpm, before=sixam)