Quote - after 8 hours..

That's a Poser reflex! Render times in Lux are extremely variable; You might get in 10 minutes what on another picture might require a day, on the same computer. Obviously using different computers you'll get another difference factor of 1000+.

The unit for render "quality" in Lux is the S/px value Lux displays on the bottom. It means "Samples/pixel", and is the number telling you how thoroughly Lux has worked on an average pixel. That's the only really objective thing you know about a render. (More is obviously better, and values of 20000 S/px for high-end production shots are apparently pretty common.)

All this to say, 8 hours could get you to a million S/px (on a 32-core renderfarm!), or just to meager 200-300 S/px (on my computer...).