Most of the problems on mine either showed up right away, or after moving them around a bunch. I would find problems after running for 5-6 hours, but i think it was more from me moving the lights around and trying to see if any node movement banging around would cause issues. I would take them while they were running and pick them up and drop them about 6 inches off of the floor and repeat. (windy mega tree simulation)
Every time I found a problem I would cut out the offending node, and burn them in longer. I think they all got about minimum of 12 hours each.