BIB, yes, good point. But I suppose we only have the departure time of 3.10am being quoted by the police because they have looked at the later timings of Sally, en route, and have worked backwards, time wise, and taken the last sighting of Sally, by her husband, as her departure time from her home.
But, it could be possible that Sally did not leave until perhaps 20 minutes or so later - so 3.30am - by which time her husband could have gone back to sleep. Having said that, she does seem to have been fully aware of what she was doing, fleece, jacket and boots put on, so no doubt she would also take care to close the door quietly, so as not to wake her husband.
