After getting the Xhifhut Head while helping a friend with Savage Blade I decided to farm the rest of these items while skilling up my NPC buddy.
Xhifhut Strings - Antican Aedilis, entered from Western Altepa D12
Xhifhut Bow - Antincan Hoplomachus outside D12 entrance to QSC. Got this 3 minutes after Strings ^^
Xhifhut Body - Antican Signifier, entered from W. Altepa J9
The body dropped last night on Firesday day (around 18:00) so I warped back to Sandy, grabbed the other three items, and tele'd back out. Peddlestox spawned at exactly 00:00 in L-7 and he placed the marker for the Treasure all the way the hell in G-11. Wait a minute, I thought to myself, G-11 in Western Aletpa Desert why does that sound so... oh, bravo Square Enix. The spot where my treasure was buried was in the EXACT MIDDLE of King Vinageroon spawn area >.<
Thankfully he didn't appear, but neither did the ??? 20:00 rolls around, and the ??? doesn't appear. 4:00 on Darksday comes, no ??? but the spot on my map where the treasure is allegedly buried is right in front of me and didn't vanish from the map as some people suggested. I continued to run around the area tabspamming until 9:00 Darksday and decided, in frustration, to check the 'net a bit more closely. Information is spotty on these quests because nobody chooses to do them, but it's my understanding that the ??? DOES NOT "spawn" between 20:00 and 4:00 which makes sense since Peddlestox doesn't mention anything about a specific time. In fact, it doesn't spawn at all. You can't target the ??? as you run near it (like you can with quest & mission ???s) but rather, you have to position yourself directly on top of the marker on your map, hit the target key, and if you're standing in the right spot you'll target (but not see) a ???. With the ??? targeted, but no cursor over it, I used a pickaxe and dug up a "strange, wooden crate" at 14:29 on Darksday- well outside of the 20:00 - 4:00 window
I did get the Sand Mantle, 4 other random items, and 10,000 gil so I'm not reallly complaining... but if you're going to do this quest, please try the method I described above before wasting an hour of your time waiting for the ??? to appear in front of you at a given time. It won't! ^^