diff --git a/metricflow/plan_conversion/dataflow_to_sql.py b/metricflow/plan_conversion/dataflow_to_sql.py
index 03ad2ec334..9dbb0d53a2 100644
--- a/metricflow/plan_conversion/dataflow_to_sql.py
+++ b/metricflow/plan_conversion/dataflow_to_sql.py
@@ -281,24 +281,23 @@ def visit_join_over_time_range_node(self, node: JoinOverTimeRangeNode) -> SqlDat
         input_data_set = node.parent_node.accept(self)
         input_data_set_alias = self._next_unique_table_alias()
 
-        metric_time_dimension_spec: Optional[TimeDimensionSpec] = None
         metric_time_dimension_instance: Optional[TimeDimensionInstance] = None
         for instance in input_data_set.instance_set.time_dimension_instances:
             if instance.spec == node.time_dimension_spec_for_join:
                 metric_time_dimension_instance = instance
-                metric_time_dimension_spec = instance.spec
                 break
+        assert (
+            metric_time_dimension_instance
+        ), "Specified metric time spec not found in parent data set. This should have been caught by validations."
 
-        assert metric_time_dimension_spec
         time_spine_data_set_alias = self._next_unique_table_alias()
 
         metric_time_dimension_column_name = self.column_association_resolver.resolve_spec(
-            metric_time_dimension_spec
+            metric_time_dimension_instance.spec
         ).column_name
 
         # Assemble time_spine dataset with metric_time_dimension to join.
         # Granularity of time_spine column should match granularity of metric_time column from parent dataset.
-        assert metric_time_dimension_instance
         time_spine_data_set = self._make_time_spine_data_set(
             metric_time_dimension_instance=metric_time_dimension_instance,
             metric_time_dimension_column_name=metric_time_dimension_column_name,
@@ -309,12 +308,12 @@ def visit_join_over_time_range_node(self, node: JoinOverTimeRangeNode) -> SqlDat
 
         # Figure out which columns correspond to the time dimension that we want to join on.
         input_data_set_metric_time_column_association = input_data_set.column_association_for_time_dimension(
-            metric_time_dimension_spec
+            metric_time_dimension_instance.spec
         )
         input_data_set_metric_time_col = input_data_set_metric_time_column_association.column_name
 
         time_spine_data_set_column_associations = time_spine_data_set.column_association_for_time_dimension(
-            metric_time_dimension_spec
+            metric_time_dimension_instance.spec
         )
         time_spine_data_set_time_dimension_col = time_spine_data_set_column_associations.column_name
 
@@ -342,7 +341,7 @@ def visit_join_over_time_range_node(self, node: JoinOverTimeRangeNode) -> SqlDat
                 [
                     time_dimension_instance
                     for time_dimension_instance in input_data_set.instance_set.time_dimension_instances
-                    if time_dimension_instance.spec != metric_time_dimension_spec
+                    if time_dimension_instance != metric_time_dimension_instance
                 ]
             ),
         )