Translation:The student is sleeping because it is Saturday.
It's usually an hour before bedtime before I get on the lessons and am wasted at times. Yesterday it was a 140 mile drive to the VA facilities for tests. Sometimes I'm so tired I can't think. If you saw what I do in one day, you'd say I was nuts. I was aleays spelling champion in school. Now I make stupid mistakes about 95% of my errors.
Well, first of all it is not exactly the "X is Y" construction, as the X (today) is only implied, and second of all, the words denoting time: yesterday, today, tomorrow and similar are adverbs*, and the version with Instrumental needs both X and Y to be noun phrases.
*OK, "jutro" and some others can be treated as nouns in some contexts, but not here anyway.
The student is asleep because it is Saturday not accepted can you please tell me my error
No error, I added it two days ago and it takes some time for the changes to go live.
Yes, that works. I mean, you made a typo (saurday) but it seems that it would still be accepted.