When you're making latkes, you can grate the potatoes up to about 3 hours ahead. They will turn pinkish brown, but they are about to be fried into golden perfection, so it doesn’t matter. As the potatoes sit, the will leech a lot of liquid; drain and discard the liquid before mixing with flour, egg, etc.
For what it’s worth: one year we made the mixture for to serve latkes to about 50 people. But just before we started to cook, smoke billowed out of the fireplace and we had to evacuate the house! By the time the firemen came, declared us safe and left, our guests were very hungry and our mixture had sat for a couple of hours. We will always ask ourselves if the latkes were better that year than any other because the mixture “rested”—or because we were all hungry by the time we finally ate.
Recipe: Basic Potato Latkes