fix issue with datetime

app.py

@@ -177,7 +177,7 @@ def get_last_refresh_time(path) -> str:
     latest_time = max([os.path.getmtime(f) for f in csv_files])
     
     # Convert to human-readable format
-    return datetime.fromtimestamp(latest_time).strftime('%Y-%m-%d %H:%M:%S')
+    return datetime.datetime.fromtimestamp(latest_time).strftime('%Y-%m-%d %H:%M:%S')
 
 
 with block: