I'm thinking that an apt title would perhaps come from within the verses, too. I love your last line, and if it were my work, I would entitle it "This Day's Grave."
The reasons? Well, it's a strong theme, the sunset as metaphor to life's end. But that it is "this" day's grave would suggest that there will be yet another day to follow. To me, it refers to allowing one's "day" (mistakes, regrets, weariness, shortcomings, etc) to be put to rest, with the hopeful notion that one's "tomorrow" will arrive bearing yet another opportunity for fulfillment, through one's own efforts and chosen direction.
You've got a wonderful poem going here! Keep writing!