simplifying code according to the review

Author: ayushjariyal

src/aiida/orm/implementation/storage_backend.py

@@ -484,14 +484,11 @@ def get_orm_entities(self, detailed: bool = False) -> dict:
             )
             data['Nodes']['process_types'] = [p for p in process_types if p]
 
-            first_time = QueryBuilder(self).append(Node, project=['ctime'], tag='node').order_by({'node': {'ctime': 'asc'}}).limit(1)
-            last_time = QueryBuilder(self).append(Node, project=['ctime'], tag='node').order_by({'node': {'ctime': 'desc'}}).limit(1)
+            first_time = QueryBuilder(self).append(Node, project=['ctime'], tag='node').order_by({'node': {'ctime': 'asc'}}).first(flat=True)
+            last_time = QueryBuilder(self).append(Node, project=['ctime'], tag='node').order_by({'node': {'ctime': 'desc'}}).first(flat=True)
 
-            ctime = first_time.first()
-            mtime = last_time.first()
-
-            data['Nodes']['first_created'] = str(ctime[0]) if ctime else None
-            data['Nodes']['last_created'] = str(mtime[0]) if mtime else None
+            data['Nodes']['first_created'] = str(first_time) if first_time else None
+            data['Nodes']['last_created'] = str(last_time) if last_time else None
 
 
         query_group = QueryBuilder(self).append(Group, project=['type_string'])