What they said^^^^^^^
I would only add that it doesn't hurt anything to do a diacetyl rest except for a couple of extra days in the process. Yeast react differently and some will produce diacetyl even at low temps. Bringing the beer up to 60-65F will speed up the cleaning process and help finish the beer to FG. If you pitch enough yeast in well aerated wort you may not need to do this, but like I said, it doesn't hurt....if you are unsure, I would do it.
It's a cheap insurance policy IMHO.