Why does the story start in April?
As T. S. Eliot said, "April is the cruelest month."
April is supposed to be the month of resurrection, rebirth, and rejuvenation. It's the month of Easter, the holy celebration of Christ's death and resurrection. It's spring flowers. It's mating season. It's planting season.
But all of this is for naught in 1984. The setting is symbolic of just the opposite: sickness, morbidity, decay, fear, and suffering.
It was a bright cold day in April, and the clocks were striking thirteen.
It is the month of cold craziness. Time is out of whack here. Fear and propaganda have destroyed man's ability to love and worship. It is, as Eliot said, a cruel month. Its promises are false promises:
But this evening as he came out of the Ministry the balminess of the April air had tempted him. The sky was a warmer blue than he had seen it that year, and suddenly the long, noisy evening at the Centre, the boring, exhausting games, the lectures, the creaking camaraderie oiled by gin, had seemed intolerable. On impulse he had turned away from the bus-stop and wandered oﬀ into the labyrinth of London, ﬁrst south, then east, then north again, losing himself among unknown streets and hardly bothering in which direction he was going.
So Orwell, like Eliot, uses April to tease the modern man. He is setting Winston and his readers up for hope of a rebellion that will never come, for hope of a relationship that will never develop, for hope of a hero that will be only tortured.