Setting is comprised of time and location, so your question is really about setting. The setting of Anne Brontë's novel has some interesting aspects. The first is that the location of the action is never clearly stated. We know it is set in the countryside in England as locations are identified as "-shire," with "-shire" being a very English location suffix:
'But why have you called it Fernley Manor, Cumberland, instead of Wildfell Hall, ___shire?’
Anne Brontë, like her sister Charlotte Brontë (Jane Eyre), uses aspects of location, like weather and terrain, as symbolic of character interactions in the plot. This is a little different from how others may use these aspects as most often these are used to set the general mood of the story and as a technique of foreshadowing.
Yet, in this story, as in other Brontë stories, the beginning setting aspects may bear little or no relation to the ending aspects. This makes the effect of location on the story very great as these particulars change as the interaction between major characters changes. For example, in Wildfell, we start with gloomy "fields, one cold, damp, cloudy evening towards the close of October," then move to "the shadow of our noble ash-trees by the water-side, with their branches gently swaying in the light summer breeze," and end with:
that beautiful half-blown Christmas-rose that grew upon the little shrub without, just peeping from the snow that had hitherto, no doubt, defended it from the frost, and was now melting away in the sun
Time is interesting because we see on the last page of the story that Gilbert Markham is writing on June 10th, 1847. Yet, the opening of the story identifies the time of action as October, 1827. While the story is told in chronological order, with events following others by which they are caused or precipitated, the story is told to Halford, a friend of Gilbert's, twenty years after the events as the fulfillment of a promise to Halford:
Now, Halford, I bid you adieu for the present. This is the first instalment of my debt.
In addition, we see that Gilbert is writing from Staningley, England. How the epistolary structure affects the story is that the letter operates as a frame and provides a flashback to an earlier and more eventful time. The narrator can speak from recollection and describe conversations and emotions and events as he remembers them. As a side note, critics generally agree that Anne Brontë does not succeed in producing a male's voice for Gilbert; they generally agree that the speaker sounds like a woman instead of the man described. This, of course, would indicate that Brontë couldn't separate her own personality from the narrative well enough to convincingly produce a masculine character.