"I work on Saturdays."
に is normally used when 1) describing going to a place e.g レストランに行きます。'I go to a restaurant' or 2) saying an exact time (e.g 10:49) or day. However you dont use に when saying 'today' or 'tommorow'. The question you may have seen before may have used は as a particle in the way as 'As for ..... は, I will .....' idk whether that makes sense. Hope that helped.
This might sound weird or even be wrong, but it's the way I figure out when to use に: when you're talking about an specific period in time. Like -very- specific. Like in the examples above, or when we leard to tell the time, we would use に to say we wake up at 8 o'clock, that's specific. "Today" or "tomorrow" might change acording to when the sentence is said, but saturdays are always saturdays (??? I swear it makes sense to me). So for hours, dates, days of the week, whenever you wanna specify that something is happening. In this case, work. When? Saturday. I could be so wrong though, someone please help.
So it's a bit like when we use が instead of は to be more specific?
飛行機は大きいです。Airplanes (in general) are big.
But: ご飯がつめたい。This rice in particular is cold (because it wouldn't be accurate to say rice in general is cold)
So in this example, we're saying that we're working on this particular Saturday instead of Saturdays in general.
Have I got that right?
Yes and no. It only holds if there is no other context present. It holds based on the following rules "Use は for general statements and が for new information on the subject." However, it is dangerous to assume this because Japanese is heavily context-based.
I have copied the followings from my answer to a similar question on the discussion page of ごはんはたべません:
I have seen quite a few of saying は is general and を is specific, but actually it does not have this implication.
Look at these examples
Suppose there are a plate of rice and a plate of pasta on the table. One may say - ご飯は食べませんが、パスタは食べます。 This translate to - I don't eat the rice but I eat the pasta. Therefore は is used with something specific in this case.
Suppose you are busy and don't have time for lunch. 今日はご飯を食べません。明日は食べます。 I don't eat rice today. I will eat tomorrow. This is general and not specific to a particular dish.
When I look for whether to use は, I ask these questions.
- Do I have something to compare with the clause or noun before the は?
- Do I need to stress the negative clause that follows?
- Do I want to explain the properties of the subject?
If any of these is yes, the I will use は.
Only certain time related nouns do not follow に as I can think of: 今日、昨日、明日、おととい、あさって、毎◯（e.g. 毎週、毎日）、いつ. I think the English in the Genki textbook corresponds to these.
All others should be able to append に, including 土曜日. It does not really matter whether it is a regular interval or not. So 毎週はたらきます but 毎週の土曜日（に）はたらきます (に is optional).
Assuming I understood what you meant, I think 毎 should be used.
★ 毎 (まい) - prefix meaning "every"/"each".
I work Saturdays:
I am going to work on Saturday:
【on Saturday】【[i am] going to work】
- Can also be 土曜日は働きます
Yes they are basically the same. はたらくis a verb and しごとis a noun. So one is working and the other is work. します( dictionary formする) is added to しごとwhich is the verb "to do". To basicly say i am doing work. It might have counted it wrong because it wanted the partical を(this particle is left out, with します, as you get more casual with speaking and sometimes the app lets you not put it in). しごと を します is what i would stick with。
I was actually going to say no but then I looked it up myself. It appears that you can. Usually they may shorten from the full name *nichiyoubi" to just "nichiyou". Less commonly they will shorten to the first kanji but since thise inital kanji are their own words it usually only works on things that are going to have the days on them specifically, like a calendar or a clock. I'd also say that if you are naming a bunch of days in a row then sometimes it will shorten them so they don't have to say " 曜日" after every single one. Herrs a link: https://www.japanesewithanime.com/2017/03/weekdays-in-japanese.html?m=1