Generally for "good" renders I set up a ridiculous number like Bantha, 600 or 999 samples, and use progressive mode. I look in an hour and if it's clean I stop. I look in 4 hours and if it's clean I stop. I look a day later and if it's clean I stop. Otherwise I just let it run and don't worry about guessing the right number of samples. Once you've committed to 24 hours, another 12 is nothing. But if you auto-stop at 24 hours, another 12 actually requires another 36. That sucks big time.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)