Well, if you pitched the yeast at fermentation temperature, you may not even need a diacetyl rest anyway. I sometimes don't, expecially with that yeast.
I'd leave it at fermentation temperature, and if it needs a d-rest later, you can always do it later. Actually, even at fermentation temperature, the yeasts will clean up diacetyl, too, if given enough time. To do a d-rest before 75% of the fermentation is done isn't a good idea- but you can always do it later if you need to.
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