The average rainfall in this place is 9000 mm per year and the sky is covered by clouds on about 300 day. Therefore such sunset situations are quite rare at the West Coast of New Zealand.
When I came to this spot at Lake Matheson the syk was was partly cloudy and there was no sunlight on Mount Tasma. So I set up my tripod and camera and waited as I could not see the sun from my position. But suddenly the light got stronger and for just a few minutes Mount Tasman was lit by the setting sun.