In the second paragraph of chapter three Golding describes Jack as he is hunting; "His sandy hair, considerably longer than it had been when they dropped in, was lighter now; and his back was a mass of dark freckles and peeling sunburn." Chapter four describes Piggy's body as being "golden brown." And in chapter five when Ralph prepares to meet with the boys after the fire has gone out, his clothes are described as "stiff like cardboard, and unpleasant." These lines indicate that the boys have been on the island long enough for their hair to grow substantially longer and for it to have been bleached by exposure to the sun. Their bodies have also tanned from being in the sun constantly, and their clothes are filthy and stiff with grime and dirt. Although Golding doesn't give a specific time frame that the boys have been on the island, the reader can assume from the descriptions that it has been a several weeks.