How far in advance can sweet potatoes be peeled?
Speaking as someone who's had to prep ahead two garbage barrels of sweet potatoes for a giant gumbo event:
If you're just peeling them a few hours ahead, then just hold them whereever. Unlike russet potatoes, sweet potatoes (especially garnet yams) do not turn brown or lose texture on exposure to air.
If you're going to be holding them for a couple days, then drop them in cold water and refrigerate it. Or drop them in ice water and add more ice about twice a day (this is what we had to do, it took 2 days to prep all the ingredients). Wrapping them tightly in plastic wrap might also work, but I haven't tried it.