Day and night cycle of grotto-heaven is a phenomena that accur because of high amount of dao mark (specially light and dark path dao mark).

But if a grotto-heaven is of dark path then because of its high concentration of dark path dao mark there will only be night there.

even if dark path grotto-heaven has little bit of Light path dao mark these light path dao mark will be suppressed almost completely if not absolutely.

At most these light path dao mark may create few little auroras in the dark sky of dark path grotto-heaven.

As such Light path grotto-heaven will also have only day because of its High concentration of light path dao mark.

As for little bit of dark path dao mark that these light path grotto-heaven may have are going to be suppressed almost completely if not absolutely.

At most there probably be few small phenomena because of dark path dao mark but that's it.

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ask in comment If you have any questions or want to highlight any mistake or fact that I may have overlooked.