Learn Hardcore Croatian: Vlak dolazi točno u šest, pa nemoj kasniti. - The train comes exactly at six, so don’t be late.

Pa is a coordinating connector that often means so/and then/and. Here it links the first clause to the advice in the second: cause → consequence. It also makes the command sound a bit softer and more conversational than a bare imperative. Alternatives with a similar meaning include zato (therefore/that’s why) and more formal stoga, but pa is the most neutral-colloquial choice.

Is the comma before pa correct?

In careful standard Croatian, you normally do not put a comma before pa: Vlak dolazi točno u šest pa nemoj kasniti. Many people do insert a comma in everyday writing to mark a stronger pause or to highlight the result, as in your sentence. In formal writing, prefer no comma.

Why is dolazi (present) used for a future/scheduled event?

Croatian uses the present tense of an imperfective verb for scheduled or timetabled events, just like English does (The train arrives at six). Dolazi (from dolaziti, imperfective) is natural and neutral for a planned arrival. You could also say:

Vlak stiže u šest (using perfective stići; common for a single, concrete arrival).
Vlak će doći u šest (future with će + infinitive; explicit future, a bit heavier).

What’s the difference between dolazi, stiže, and će doći?

Dolazi (imperfective present): scheduled or habitual arrival; also the process of coming.
Stiže (perfective present): a single, concrete arrival; in perfective aspect the present often has a future-like meaning.
Će doći (future): explicit future, often when you’re stating a plan or prediction. All three can be correct; the nuance is about aspect and style.

Why točno and not točan? Where can točno go?

Točno is an adverb (exactly) modifying the time expression, not the noun vlak. Točan is an adjective (exact), which would modify a noun, e.g., točan sat (an accurate clock). Typical placements:

Vlak dolazi točno u šest (most common)
Vlak dolazi u točno šest
Točno u šest vlak dolazi (fronted for emphasis)

Does u šest take a specific case, and can I say u šest sati?

Clock time after u takes the accusative. With numbers like šest, the form looks the same in nominative and accusative, so you don’t see a change. Both are fine:

u šest
u šest sati (more explicit, literally at six hours)

How do I say “at 6 p.m.” to avoid ambiguity?

Add a time-of-day word:

u šest navečer (in the evening)
u šest ujutro (in the morning)
u šest popodne or poslijepodne (in the afternoon) Or use the 24-hour clock:
u osamnaest sati (at 18:00)

What’s the nuance between kasniti and zakasniti?

Kasniti (imperfective): to be late (as an ongoing state or general habit). Nemoj kasniti = don’t be late (in general/this time).
Zakasniti (perfective): to end up being late (a single completed event). Nemoj zakasniti = don’t end up being late for this one occasion; a bit more event-focused.

Is Ne kasni! also acceptable, or must I use Nemoj kasniti!?

Both are used. Nemoj kasniti! (nemoj + infinitive) is the standard, very common way to make a negative imperative in Croatian and often feels a touch softer. Ne kasni! also occurs in speech and is perfectly understandable. For perfective verbs, the negative imperative is most naturally nemoj + infinitive: Nemoj zakasniti! (rather than Ne zakasni!, though you will hear that too).

How do I address more than one person or be polite?

Use the plural/polite form:

One person (informal): Nemoj kasniti.
More than one person / polite: Nemojte kasniti. You can also soften with Molim te (please, informal) or Molim vas (please, polite): Molim vas, nemojte kasniti.

Could I drop pa and just use two sentences?

Yes. You can write: Vlak dolazi točno u šest. Nemoj kasniti. If you want one sentence without pa, use a dash or semicolon: Vlak dolazi točno u šest — nemoj kasniti. Don’t join two independent clauses with just a comma in formal writing.

Does pa make the command softer?

Yes. Pa often conveys a gentle, conversational link (so…), which can make nemoj kasniti sound less brusque than a standalone imperative.

Are there synonyms for točno here?

Yes, common equivalents are:

baš u šest (exactly at six)
upravo u šest (right at six) All are natural: Vlak dolazi baš/upravo u šest.

Is vlak the usual Croatian word for train? What about voz?

In standard Croatian, vlak is the normal word. Voz is standard in Serbian; in Bosnia you’ll hear both. In Croatia, stick with vlak.

Do I need to write the diacritics in točno and šest?

Yes. Croatian uses diacritics as separate letters:

č in točno (not c)
š in šest (not s) Omitting them in casual texting is common, but in proper writing you should include them.

Can I reverse the order to lead with the warning?

Absolutely. Nemoj kasniti, vlak dolazi točno u šest. This puts the emphasis on the instruction first; the meaning and grammar remain the same.