The episode centres on a pheasant shoot, which means it must be set between 1 October and 1 February as that's when the law says you can shoot pheasants. However filming clearly happened in late April/early May, as bluebells are in flower, and the plot depends on another plant being in flower that would not be around during the pheasant season.
Near the 12 min mark Ruth's face is a different color than her neck. Her makeup was not applied in or tested in sunlight.