Heh, my impatience kicks in is usually at one day. Aka, I start the render in the early evening, go to bed, get up, if it's still rendering, I hope it's not too much longer, go to work and if it's STILL rendering, then I get grumpy. I've gone 3 days before I finally said enough, and reworked the piece to go faster. My challenge image last month was potentially a 1 week render... Sorry, I'll fake the volumetrics first. Does rendering to disk work faster? I can't remember.