The anonymity of the village signals its universality. It adds to the horror of the story that we can imagine the lottery taking place anywhere, in any small town we might know. We can't confine the violence of the lottery to a specific area or a certain set of people: Jackson's critique is America-wide. The references to other towns that hold lotteries contribute to our sense that Jackson isn't talking about any one community, but is instead critiquing society as a whole.
As for the lottery's temporal setting – a day in mid-summer – it indicates a period of unconstrained growth and reckless abandon. The children are testing the freedoms of summer. The flowers are "blossoming profusely." The grass is "richly green." We might read the village's ritual murder as its method of pruning excessive growth. Many critics point out that the summer solstice was a popular time of pre-historic ritual, and that the lottery's timing is a subtle gesture to earlier primitive rituals.