How is anachrony used in Mrs Dalloway?

Anachrony is related to anachronism, which essentially covers anything in a literary work that is "against time." Anachronism is common in medieval works, where chronological time was not a cultural value. In this aesthetic, human events were often viewed as elements that would be better understood from the divine's timeless perspective. This is largely the argument of Boethius, who was tremendously influential in the Middle Ages.
In the Modern era a similar, though secular, view of time begins to emerge, largely through the influence of Einstein's theory of relativity and the space-time continuum. Woolf experimented often with elements of Time, Space, and Consciousness.
In Mrs. Dalloway, Clarissa and Septimus both return repeatedly to a past moment that then enters their present consciousness. Gertrude Stein called this continuous present, for the life of the mind is as palpable as the life of the body, and these thoughts are not merely memories. In the narrative, these moments look like flashbacks but they function to amplify the events of the single day during which the novel is set.
This technique supports Woolf's overarching concern with how humans create and maintain connections, how past selves are kept vibrant, and how memory intrudes as an animating force within one's ongoing journey of life.