Ako ondje opet prenoćimo, odjavit ćemo se ranije da stignemo na vlak bez žurbe.

Because after ako (if), Croatian often uses the present tense to talk about a future possibility.

So:

• Ako ondje opet prenoćimo = If we stay there overnight again
• not literally If we are spending the night there again

Here prenoćimo is the 1st person plural present form of the perfective verb prenoćiti. With ako, that present form commonly refers to a future event.

This is very natural in Croatian:

• Ako dođe, javit ću ti. = If he comes, I’ll let you know.
• Ako stignemo na vrijeme, sve će biti u redu. = If we arrive on time, everything will be fine.

So even though the form is present, the meaning is future because of the context.

Both mean there.

• tamo is more common and conversational
• ondje is a bit more neutral, literary, or slightly more formal

In many contexts they are interchangeable:

• Ako tamo opet prenoćimo...
• Ako ondje opet prenoćimo...

Both are correct. Using ondje just gives the sentence a slightly more careful or polished tone.

Prenoćimo comes from prenoćiti, which means:

• to spend the night
• to stay overnight

So it does not simply mean sleep in general. It means staying somewhere for the night.

Examples:

• Prenoćili smo u hotelu. = We stayed overnight in a hotel.
• Možemo li ovdje prenoćiti? = Can we stay overnight here?

In your sentence, it suggests staying one night at that place.

Opet means again.

In this sentence:

• Ako ondje opet prenoćimo = If we stay there overnight again

It tells you that this would not be the first time.

Its position is fairly flexible, but different placements can sound slightly different in emphasis:

• Ako ondje opet prenoćimo...
• Ako opet ondje prenoćimo...
• Ako prenoćimo ondje opet... ← much less natural

The version in your sentence is very natural. It places opet close to the action being repeated.

This is the future tense of odjaviti se.

Breakdown:

• odjaviti se = to check out / sign off / unregister oneself, depending on context
• ćemo = auxiliary used for the future, meaning we will
• odjavit ćemo se = we will check out

So the structure is:

• infinitive stem / main verb part: odjavit
• future auxiliary: ćemo
• reflexive clitic: se

Croatian future tense often looks like this:

• doći ćemo = we will come
• vidjet ćemo = we will see
• odjavit ćemo se = we will check out

Because the verb is odjaviti se, a reflexive verb.

In this context, odjaviti se means to check out—for example, from a hotel, hostel, or accommodation.

Without se, odjaviti usually means to unregister something/someone or to sign something off, depending on the context.

Compare:

• odjaviti se iz hotela = to check out of a hotel
• odjaviti računalo = to disconnect / unregister a computer (depending on context)

So se is part of the dictionary form of the verb here and cannot be omitted.

Both patterns exist in Croatian, but odjavit ćemo se is the standard neutral future construction when the verb stands at the beginning of the clause.

Croatian future I is commonly formed like this:

• čitat ću
• ići ćemo
• odjavit ćemo se

In practice:

• Odjavit ćemo se ranije sounds natural and standard.
• Ćemo se odjaviti ranije is not the normal standard order.

If another word comes first, the auxiliary can appear after that first element because Croatian clitics tend to go in second position:

• Sutra ćemo se odjaviti ranije. = Tomorrow we’ll check out earlier.

So in your sentence, odjavit ćemo se is exactly what you would expect.

Because ranije means earlier, while rano means early.

That distinction matters here:

• odjavit ćemo se rano = we will check out early
• odjavit ćemo se ranije = we will check out earlier

The sentence suggests a comparison, even if it is only implied:

• earlier than usual
• earlier than we otherwise would
• earlier than the normal checkout time, depending on context

So ranije is the better choice if the idea is earlier rather than simply early.

Because Croatian very often uses da + present tense to express purpose or intended result.

Here:

• da stignemo na vlak = so that we catch/make the train

This is a very common pattern:

• Došao sam da pomognem. = I came to help.
• Požurili smo da stignemo na vrijeme. = We hurried so that we would arrive on time.

English often uses an infinitive:

• We left early to catch the train

Croatian often prefers:

• ...ranije da stignemo na vlak

So this is a normal Croatian way of expressing purpose.

Stići means to arrive, to make it, or to catch depending on context.

In this sentence:

• stignemo na vlak means we catch the train / we make the train

Literally, it is something like:

• arrive in time for the train

Croatian uses na with forms of transport in expressions like this:

• stići na autobus = to make the bus
• stići na tramvaj = to catch the tram
• stići na vlak = to catch the train

So na vlak is the normal expression here.

Vlak is in the accusative singular after na, because it expresses motion toward a goal or target.

For masculine inanimate nouns, the accusative singular is usually the same as the nominative singular.

So:

• nominative: vlak
• accusative: vlak

That is why the form does not change.

Compare with another masculine inanimate noun:

• autobus → na autobus

But with a feminine noun you would see a clearer change:

• na stanicu = to the station

Bez žurbe means without hurry, or more naturally in English, without rushing / without any rush.

The preposition bez always takes the genitive case.

So:

• žurba = hurry (nominative)
• bez žurbe = without hurry (genitive)

This is a very useful pattern:

• bez problema = without problems / no problem
• bez šećera = without sugar
• bez žurbe = without rushing

Yes, in this sentence bez žurbe sounds much more natural.

• bez žurbe = idiomatic, simple, everyday
• ne žureći = grammatically possible in some contexts, but much less natural here

Croatian often prefers a noun phrase like bez žurbe where English might use an -ing form:

• without rushing
• without hurrying

So da stignemo na vlak bez žurbe is smooth and idiomatic.

Yes, the order can be reversed.

The sentence as given is:

• Ako ondje opet prenoćimo, odjavit ćemo se ranije...

This is very natural: first the condition, then the result.

You could also say:

• Odjavit ćemo se ranije ako ondje opet prenoćimo...

That also means the same thing:

• We’ll check out earlier if we stay there overnight again...

The version with ako first often sounds a bit more organized or slightly more formal in written language, but both are common.

Because the conditional clause comes first.

In Croatian, when a subordinate clause such as an ako clause precedes the main clause, it is normally separated by a comma:

• Ako dođeš, nazovi me.
• Ako bude kiše, ostat ćemo kod kuće.
• Ako ondje opet prenoćimo, odjavit ćemo se ranije...

If the ako clause comes after the main clause, the comma is often omitted:

• Nazovi me ako dođeš.

So the comma here is standard punctuation.

Yes, very important.

Croatian verbs often come in aspectual pairs, and here the aspect helps show the meaning clearly.

• prenoćiti is perfective: to spend the night, as a completed event
• stići is also typically used as a perfective verb: to arrive/make it successfully
• odjaviti se is perfective as well in this context: to check out, a completed action

That fits the sentence because it talks about single, completed actions:

• if we stay overnight
• we will check out
• so that we catch the train

If imperfective verbs were used instead, the meaning would shift toward process, repetition, or general activity rather than one completed event.

Yes, it could.

• opet = again
• ponovno = again, often a bit more formal or more neutral in style

So:

• Ako ondje opet prenoćimo...
• Ako ondje ponovno prenoćimo...

Both are correct.
In everyday speech, opet is usually more common.

Yes, it sounds natural and idiomatic.

A native speaker might also say similar things such as:

• Ako ondje opet prenoćimo, odjavit ćemo se ranije da stignemo na vlak bez žurbe.
• Ako tamo opet prespavamo, odjavit ćemo se ranije da stignemo na vlak bez žurbe.
• Ako ondje ponovno prenoćimo, odjavit ćemo se ranije kako bismo stigli na vlak bez žurbe.

The original sentence is perfectly good Croatian. It is clear, grammatical, and natural.