I spent a few days doing the 1-day time-traveling trick to get most of the art, and then I was still missing 10 or so pieces, but fortunately was able to trade for them on this forum to complete the art exhibit.
What I observed when time-traveling for the art was that it seems unlikely to acquire it all without trading. As others have mentioned, the game will continue to show you duplicates and fakes, so while at first you are routinely getting new art, once you need the last 10-20, the RNG does not seem to be in the player's favor.
Redd only appears 26 times or so each year with no guarantee you're going to get a new piece when he's there. There are 43 pieces overall, so even with *very* fortunate RNG, I think it would take a few years to get them all without trading, and that's not even guaranteed.
What I observed when time-traveling for the art was that it seems unlikely to acquire it all without trading. As others have mentioned, the game will continue to show you duplicates and fakes, so while at first you are routinely getting new art, once you need the last 10-20, the RNG does not seem to be in the player's favor.
Redd only appears 26 times or so each year with no guarantee you're going to get a new piece when he's there. There are 43 pieces overall, so even with *very* fortunate RNG, I think it would take a few years to get them all without trading, and that's not even guaranteed.