Isehara city answers the question directly on its own site: it depends where you stand, but the colour arrives in the middle of November and holds through the end of the month. On a mountain that caveat matters, because the top and the bottom are not on the same schedule and can look like different weeks on the same day.

Oyama sits in the Tanzawa-Oyama Quasi-National Park and has been an object of worship in its own right for centuries. The image most associated with it is the approach to Oyamadera, where maples line the stone steps. Looking up, the colour closes over the stairway; looking back down on the descent, it opens out again over the valley. The two views are worth treating as separate.

The lower shrine of Oyama Afuri also has maples, and from its terrace Sagami Bay lies open below. In the last third of November both the temple and the lower shrine are lit after dark, so the leaves and the lights of the plain appear together.

The Edo period had a custom of pilgrimage to this mountain, and the present approach follows that route. It is stairs most of the way. Choose footwear accordingly, and note that the cable car does not remove the climbing so much as move where it starts.