Post Office – Newton Stewart, High Street – Opening Hours & Branch Details Post Office is proud to be situated at 17 High Street, about 12.70 miles south from the centre of Newton Stewart (by South Street). This branch is situated perfectly to serve those from the locales of Sorbie, Portyerrock, Whithorn, Garlieston, Castlewigg, Galloway House and Isle of Whithorn. Today (Friday), business times begin at 9:00 am and end at 5:30 pm. Here, on this page, you will find additional information about Post Office Newton Stewart, High Street, including the working hours, local directions and product ranges.