Learn Hardcore Japanese: watasi ha syuumatu ni osoku okimasu.

は is the topic marker. It tells the listener that “as for me” you’re talking about your own habit. が would mark 私 as the subject and is more neutral or used for emphasis (“I” specifically did it, not someone else). In a simple statement about yourself, 私は…起きます is more natural.

Why is に used after 週末?

に marks a specific time when something happens. Here 週末に means “at the weekend” or “on weekends.” Without に, 週末 can sometimes function as a general adverb (“weekends”), but adding に makes it clear it’s a time point.

What does 遅く mean in this sentence and why doesn’t it end with い?

遅く is the adverbial form of the i-adjective 遅い (slow/late). To modify the verb 起きます (“wake up”), 遅い changes to 遅く. It means “late (in the morning).” If you kept 遅い, it would not properly modify the verb.

Why is 遅く placed before 起きます?

In Japanese, adverbs (like 遅く) typically come directly before the verb they modify. So 遅く起きます literally means “wake up late.”

What form is 起きます and what tense does it express?

起きます is the polite non-past form of 起きる (“to wake up”). It can express either present or future habitual action. Here it describes your regular weekend routine (“I wake up late on weekends”).

Can I omit 私は and just say 週末に遅く起きます?

Yes. In Japanese, the subject is often dropped if it’s clear from context. 週末に遅く起きます is perfectly natural if you’ve already established that you’re talking about yourself.

Is 週末に here referring to “this weekend” or “weekends” in general?

It refers to your general habit of waking up late on weekends (every weekend). If you meant specifically “this weekend,” you’d often add context or a word like 今週末に (“this weekend”).

How would I say the casual/plain form of this sentence?

In plain form you drop the ます, so it becomes 私は週末に遅く起きる。 Or simply 週末に遅く起きる。 if you omit the topic.