The sunset you were seeing didn't happen 8 minutes ago. Sunsets are an interaction of the sun with your perspective position on earth and line of sight. The sunset was happening right then -- the light that was involved in the sunset had been emitted from the sun 8 minutes ago. The last blip of the light you saw disappear over the horizon was a view of a corner of the sun from 8 minutes ago, but the sunset was happening essentially at that moment. </pedantic>