Learn Hardcore Chinese: wǒ xiànzài yào shàngbān le, nǐ xiàwǔ zài lái. - I need to go to work now; come again in the afternoon.

Sentence-final 了 = new situation/change (e.g., 天黑了 “It’s gotten dark.”).
Verb-attached 了 (after a verb) = completed action (e.g., 我吃了饭 “I ate.”). In this sentence, the 了 is sentence-final, not verb-attached.

Can I omit 了 and just say 我现在要上班?

You can, but it slightly changes the feel.

With 了: imminent/it’s time now; a gentle “I’ve got to head to work now.”
Without 了: more neutral or general, like “I have to work now/these days,” without the same “it’s time” push.

Does 要 here mean “want to,” or “going to/have to”?

Here 要 means “be going to/need to,” not “want.” Context (work + 现在 + sentence-final 了) forces the “it’s time/going to” reading. If you want to clearly say “want to,” use 想: 我想去上班 (“I want to go to work”).

Why not say 要去上班 instead of 要上班?

Both are fine.

要上班了 emphasizes the start of one’s shift/status (being at work).
要去上班了 adds the motion “go,” highlighting physically going to the workplace. Everyday speech uses either depending on what you want to emphasize.

Why is 现在 after 我? Could I say 现在我要上班了?

Both are natural:

我现在要上班了 (Subject + time) — very common.
现在我要上班了 (Time first) — puts a bit more emphasis on “right now.” Avoid 我要现在上班了 in this meaning; it sounds odd.

What exactly does 上班 mean, and how is it different from 工作?

上班: attend/be on duty/go to one’s shift; it’s about being at work according to schedule. E.g., 我九点上班 (“I start work at 9.”), 今天不上班 (“I’m off today.”)
工作: to work/do work; also “job” as a noun. E.g., 我在工作 (“I’m working.”), 找工作 (“look for a job”). In this sentence, 上班 fits better because it’s about starting the shift now.

What does 再 mean in 你下午再来, and why not 又?

再 = “again/later, next time,” generally for future or planned repetition: 你下午再来 (“Come again this afternoon.”).
又 = “again” for past or present, often something has already (re)occurred: 你下午又来了 (“You came again this afternoon,” implying it happened).
还 = “still/yet/also,” not used for “do it again later.”

Where does 再 go relative to the time word? Is 你再下午来 OK?

Use Subject + Time + 再 + Verb:

Correct: 你下午再来.
Incorrect/unnatural: 你再下午来 (再 modifies the verb, not the time word). You can expand the verb phrase: 你下午再来一次 (“Come one more time this afternoon.”).

Should it be 来 or 回来 in the second clause?

来: “come (to where I am).” 你下午再来 is a natural “Come again this afternoon.”
回来: “come back (return).” Use it if both of you treat the speaker’s place as the “home base”: 你下午再回来.
去: “go” (away from the speaker). 你下午再去 would mean “go there again this afternoon,” not “come (to me).”

Do I need 吧 to sound polite in 你下午再来?

Not required, but 吧 softens it into a suggestion: 你下午再来吧 (“Why don’t you come again this afternoon.”). In service language, you might also hear 请下午再来 (“Please come again this afternoon.”).

Why is there a comma between the two parts?

Chinese often uses a comma to link two closely related clauses: “I need to go to work now, (so) you come back in the afternoon.” It’s a natural coordination/sequence; each part could be a sentence on its own.

Can I drop the pronouns and just say 现在要上班了，下午再来?

Yes. Chinese often omits pronouns when context is clear. Keeping 我/你 just makes it explicit; omitting them sounds concise and natural in casual speech.

Are there other ways to say “It’s time to work now”?

Yes, with slightly different nuances:

该上班了: “It’s time to work” (it’s due/ought to).
得上班了: “I have to work now” (necessity/obligation).
快要/就要上班了: “About to start work soon,” often also with sentence-final 了.

Does 下午 mean “this afternoon” by default?

In context, yes: since the speaker is talking about “now,” 下午 is understood as the same day. If you mean another day, specify: 今天下午 (“this afternoon”), 明天下午 (“tomorrow afternoon”).

Is 上班 a separable verb? Can I say things like 上了两天班?

Yes, it behaves like a verb-object compound in many patterns:

上了两天班 (“worked for two days”),
上班时间 (“working hours”),
不上班/下班了 (“not working”/“off work”). In your sentence, it functions as a fixed verb phrase.

How do I pronounce 了 here?

It’s the neutral-tone particle le, not liǎo. So: wǒ xiànzài yào shàngbān le, nǐ xiàwǔ zài lái.