In Spanish Saturday is "sábado", sounds similar.
True, because both have the same etymology: Sabbath.
The sobota here is not in instrumental case? This is not the jest + instru (like I am a teacher) case?
It is not. If you have a sentence with two nouns or a personal pronoun and noun, the second noun becomes instrumental. In other cases (unless I've missed something) use nominative.
So sobota is not treated as noun here ? Or is there some other condition limiting the use of instrumental case here ? Thanks !
It is 'jutro' that is not treated as a noun (although it can in other contexts), but rather as an adverb.
Thank you both!