I need to double check the legislation but iirc those devices can only be used to face and clear public areas (so footpaths, estates, car parks and roads). Generally they're for loitering issues and criminal behaviour like graffiti hotspots. I don't think you can legally use them where it covers a neighbouring private space as it can affect quality of life (in this case, the private garden of next door). As for the hours of operation, I don't know whether high frequency deterrent devices are also subject to noise laws, but I suspect they are.