diff --git a/src/batcontrol/forecastsolar/baseclass.py b/src/batcontrol/forecastsolar/baseclass.py
index dfdb2c9..5035fb2 100644
--- a/src/batcontrol/forecastsolar/baseclass.py
+++ b/src/batcontrol/forecastsolar/baseclass.py
@@ -151,15 +151,15 @@ def get_forecast(self) -> dict[int, float]:
 
         # Validate minimum forecast length
         if self.target_resolution == 60:
-            min_intervals = 18  # 18 hours
+            min_intervals = 12  # 12 hours
         else:  # 15 minutes
-            min_intervals = 72  # 18 hours * 4 = 72 intervals
+            min_intervals = 48  # 12 hours * 4 = 48 intervals
 
-        max_interval = max(current_aligned_forecast.keys()) if current_aligned_forecast else 0
-        if max_interval < min_intervals:
-            logger.error('Less than 18 hours of forecast data. Got %d intervals, need %d.',
-                         max_interval, min_intervals)
-            raise RuntimeError('Less than 18 hours of forecast data.')
+        num_intervals = len(current_aligned_forecast)
+        if num_intervals < min_intervals:
+            logger.error('Less than 12 hours of forecast data. Got %d intervals, need %d.',
+                         num_intervals, min_intervals)
+            raise RuntimeError('Less than 12 hours of forecast data.')
 
         return current_aligned_forecast
 
diff --git a/tests/batcontrol/forecastsolar/test_baseclass.py b/tests/batcontrol/forecastsolar/test_baseclass.py
index 4264cc7..d778f59 100644
--- a/tests/batcontrol/forecastsolar/test_baseclass.py
+++ b/tests/batcontrol/forecastsolar/test_baseclass.py
@@ -341,7 +341,7 @@ def mock_forecast():
             mock_forecast_func=mock_forecast
         )
 
-        with pytest.raises(RuntimeError, match="Less than 18 hours"):
+        with pytest.raises(RuntimeError, match="Less than 12 hours"):
             instance.get_forecast()
 
     def test_base_class_not_implemented_errors(self, single_installation, timezone):
diff --git a/tests/batcontrol/forecastsolar/test_baseclass_alignment.py b/tests/batcontrol/forecastsolar/test_baseclass_alignment.py
index 779fdf3..40617b9 100644
--- a/tests/batcontrol/forecastsolar/test_baseclass_alignment.py
+++ b/tests/batcontrol/forecastsolar/test_baseclass_alignment.py
@@ -317,7 +317,7 @@ def test_minimum_forecast_validation_hourly(self, pvinstallations, timezone):
             mock_datetime.timezone = datetime.timezone
 
             with patch.object(provider, 'refresh_data'):
-                with pytest.raises(RuntimeError, match="Less than 18 hours"):
+                with pytest.raises(RuntimeError, match="Less than 12 hours"):
                     provider.get_forecast()
 
     def test_minimum_forecast_validation_15min(self, pvinstallations, timezone):
@@ -327,8 +327,8 @@ def test_minimum_forecast_validation_15min(self, pvinstallations, timezone):
             target_resolution=15, native_resolution=15
         )
 
-        # Set insufficient data (less than 72 intervals = 18 hours)
-        data_15min = {i: 250 for i in range(50)}
+        # Set insufficient data (less than 48 intervals = 12 hours)
+        data_15min = {i: 250 for i in range(40)}
         provider.set_mock_data(data_15min)
 
         mock_time = datetime.datetime(2024, 1, 1, 10, 0, 0, tzinfo=timezone)
@@ -338,7 +338,7 @@ def test_minimum_forecast_validation_15min(self, pvinstallations, timezone):
             mock_datetime.timezone = datetime.timezone
 
             with patch.object(provider, 'refresh_data'):
-                with pytest.raises(RuntimeError, match="Less than 18 hours"):
+                with pytest.raises(RuntimeError, match="Less than 12 hours"):
                     provider.get_forecast()
 
 
@@ -394,8 +394,8 @@ def test_scenario_1020_with_15min(self, pvinstallations, timezone):
         assert 0 in result
         assert result[0] > 0  # Should have some solar production
 
-        # Result should have many intervals (at least 72 for 18 hours)
-        assert len(result) >= 72
+        # Result should have many intervals (at least 48 for 12 hours)
+        assert len(result) >= 48
 
     def test_scenario_matching_doc_example(self, pvinstallations, timezone):
         """