The poem "To Autumn" is a progression from morning to noon and then to evening. Explain, duly elucidating on the odal hymn.

Keats's "To Autumn" is a celebration of the beauty of autumn; it asserts that we should not think of spring when autumn has it's own beauty. We should understand this framing of autumn—at least in part—against the backdrop of the traditional symbolism of the seasons: spring as birth, summer as vibrant life, and autumn as a maturity that foreshadows winter, which is death.
The symbolism of morning, noon, evening, and night can easily mirror this symbolism. Light begins, grows, shrinks, and then vanishes. Keats, however, does not paint autumn as overshadowed by the coming winter but focuses instead on it as a time of things coming to completion and describes harvest as a time of plenty. Thinking of the comparison with a human life, we can think about the choice to frame growing old as fading away toward death or, in another sense, as coming into maturity and wisdom.
We see the times of day in the poem as Keats describes the morning mists and the friendship of autumn with the "maturing sun" in the morning. Hours and hours pass as wine continues to come from the wine press. And, finally, the "soft-dying" day ends. The poem paints the passing of time as shifting from one beauty to another. If we read winter and night as symbols of death, they are not feared in the poem but are welcomed as part of the cycle of things.