The adaptive environment sampler always works, but with some environments it will give less benefit that with other.
If you use an HDRI, particularly with high contrast (strong sunlight), you will get most benefit.
If you use Corona Sun + Sky you will get almost no benefit.
If you use a solid color (be it Corona Color, 3ds Max output, or any other node), you will get no benefit whatsoever.
*By "no benefit" I don't mean that the rendering will be slower than with other samplers - I just mean that there will be no speedup which is otherwise expected.
See:
https://blog.corona-renderer.com/corona-renderer-6-for-3ds-max-released/