8 hours ? Yeah this is what stopped me from testing Luxrenderer longer - it is very slowly, so switched back to Cycles, but hope they will improve it soon!
You have almost close box with bright walls, it mean lot of high order bounces still noticeable, and you need many time to clear noise. You can speed up a lot if change wall materials to something darker. And decrease max bounce parameter to compensate CPU time. Remember, final color after N bounces is ~ pow( material_color, N), it decrease very fast for dark materials and very slow for material that close to 1.0.