With London as the play's geographical setting, many of its cultural assumptions and reference points are based in English aristocratic society. Even if the characters never leave the city over the course of the play, the countryside functions as a sort of background setting. With the end of the London season approaching, many of the characters discuss their imminent departure to their rural manors. In addition, continental Europe looms in the background as a place that characters who don't fit in—such as Lord Darlington and Mrs. Erlynne—plan to move to.
The play's temporal setting is the end of the nineteenth century. A note that occurs before Act I specifies that the play's time is "The Present." Even an audience member who is watching the play, without the script, can glean this detail from the characters' preoccupations with modernity. They don't plainly refer to life, but to "modern life"; they discuss modern women and modern men, modern wives and modern husbands; they mention modern dress and modern novels. Their conversations feel Victorian, but the twentieth century is fast approaching.
On a more minute level, each act takes place within a given interior space. The first and final acts take place in the morning room of the Windermeres' London residence. The second act takes place in their drawing room. The third act takes place in Lord Darlington's rooms. Although an audience member wouldn't be privy to this in concrete terms (but would be able to tell more or less on their own), a reader finds out before Act I that the play's action takes place over the span of less than 24 hours, "beginning on a Tuesday afternoon at five o'clock, and ending the next day at 1:30 pm." This temporal tightness makes for a busy mood, and reinforces the intensity that underlies both the action and the character development.