The prophecy is of India's freedom from British rule.
The Bird of Time was published in 1911. By then, Naidu was active in the struggle for Indian independence. Her parents were members of the Brahmo Samaj, a progressive movement for social and religious reform. Naidu's commitment to Brahmo ideals informed her vision for independent India. For Naidu, as for so many participants in the freedom struggle, independence meant not just political sovereignty, but also social renewal. Freed from the imperial yoke, India would enter a golden age, achieving harmony among all its citizens despite differences of religion, caste, gender, and language. India would awake from darkness into a new dawn, a "renascent morn".
Jawaharlal Nehru's speech to the Indian Constituent Assembly on 14th August 1947, the eve of India's independence, employs the same visionary tropes:
Long years ago we made a tryst with destiny, and now the time comes when we shall redeem our pledge, not wholly or in full measure, but very substantially. At the stroke of the midnight hour, when the world sleeps, India will awake to life and freedom. A moment comes, which comes but rarely in history, when we step out from the old to the new, when an age ends, and when the soul of a nation, long suppressed, finds utterance.
This is not to say that Nehru is consciously adopting Naidu's rhetoric. The point is rather that as Naidu's poem and Nehru's speech both illustrate, the freedom movement relied on language of prophesy to present a vision of India whose renewal into "crescent glory" was foretold.