Unfortunately the theory that Untended Graves is in the future has a few problems with it. The Shrine Handmaiden has special dialogue if you talk to her after speaking to her in the untended graves, but not any time before then (she can't remember something from the future). Ludleth makes mention of the firekeeper's eyes if you have them in your possession, one specific sentence of importance is "Tis as if it were but yesterday", which is obviously implying it happened in the past. There's also Gundyr; he acts as a test of an ashen one's strength, to see if they are worthy to seek the lords. The player chronologically defeats him in the untended graves in his true power and then once again as Iudex Gundyr when the player awakens, when he is weak, likely from already being defeated once before. The Untended Graves takes place in the past in an age of dark, before the bells of awakening have rung.