11pm any night of the week, and that's because it's the law - if you just wanted to be a good neighbour, decent human being, and not a complete **** I'd say 9-10pm.
If noise travels through the walls so much that you can't do anything without hearing it think about insulation or moving, it really is your problem - not your neighbours.
If noise travels through the walls so much that you can't do anything without hearing it think about insulation or moving, it really is your problem - not your neighbours.