"We sleep at night."

Translation: Śpimy w nocy.

[Ash473779]

What case is 'nocy' here?

[4d1n]

Locative

[Falstaff4]

"In the morning we sleep" would be Rano śpimy, correct? Then could you also write Noc śpimy for "in the night we sleep"?

[Jellei]

Because "rano" isn't only a noun (in fact it rarely is used that way), but also an adverb meaning "in the morning. "Noc" is just a noun.