Popodnevni sastanak je u četiri sata.

Popodnevni means afternoon in the sense of taking place in the afternoon.

So popodnevni sastanak means afternoon meeting.

A useful distinction is:

• popodnevni = an adjective: afternoon meeting, afternoon class, etc.
• popodne = usually an adverb/noun meaning in the afternoon or afternoon

For example:

• popodnevni sastanak = afternoon meeting
• Sastanak je popodne. = The meeting is in the afternoon.

Because it has to agree with sastanak.

In Croatian, adjectives change their form to match the noun in:

• gender
• number
• case

Here, sastanak is:

• masculine
• singular
• nominative (the subject form)

So the adjective also appears in the masculine singular nominative form:

• popodnevni sastanak

If the noun changed, the adjective would change too.

Sastanak is masculine.

A common clue is that many masculine nouns in Croatian end in a consonant, and sastanak does.

You can also see it from adjective agreement:

• popodnevni is masculine singular
• so it matches a masculine noun: sastanak

The word means meeting.

Je is the 3rd person singular present form of biti (to be).

So it means is.

In this sentence, it links the subject and the time expression:

• Popodnevni sastanak = the afternoon meeting
• je = is
• u četiri sata = at four o’clock

So structurally it works like:

• The afternoon meeting is at four o’clock.

In standard Croatian, this je is normal and expected here.

Croatian normally uses u with clock times, where English uses at.

So:

• u jedan sat = at one o’clock
• u dva sata = at two o’clock
• u četiri sata = at four o’clock

So even though u often means in or into in other contexts, with clock times it is the normal way to say at.

Because after the numbers 2, 3, and 4, Croatian uses the form sata with sat.

So:

• jedan sat = one hour / one o’clock
• dva sata = two hours / two o’clock
• tri sata = three hours / three o’clock
• četiri sata = four hours / four o’clock
• pet sati = five hours / five o’clock

So četiri sata is the correct form.

This is a very common pattern, and learners usually just memorize:

• 2, 3, 4 + sata
• 5 and above + sati

Yes, very often you can.

Both are natural:

• u četiri sata
• u četiri

The shorter version is very common in everyday speech when the meaning is obvious.

The longer version can sound a bit fuller or more explicit, but both are correct.

Because Croatian does not have articles like English a / an / the.

So sastanak can mean:

• a meeting
• the meeting

The exact meaning depends on context.

In your sentence, the meaning is understood from the situation, not from an article.

This is very normal in Croatian, and English speakers often need time to get used to it.

Yes. Croatian word order is more flexible than English word order.

This sentence could also appear as:

• Sastanak je u četiri sata.
• U četiri sata je popodnevni sastanak.
  (more marked, depending on emphasis)

The original sentence:

• Popodnevni sastanak je u četiri sata.

sounds neutral and clear.

Croatian often changes word order to shift emphasis, but the basic meaning stays the same.

A simple English-friendly guide:

• četiri ≈ CHEH-tee-ree
• sastanak ≈ SAH-stah-nahk
• popodnevni ≈ po-po-DNEV-nee
• je ≈ yeh

A few useful pronunciation points:

• č sounds roughly like ch in church
• j sounds like y in yes
• Croatian vowels are usually clear and short, without the heavy reduction common in English

So the full sentence is approximately:

po-po-DNEV-nee SAH-stah-nahk yeh oo CHEH-tee-ree SAH-tah

They are related, but not exactly the same in structure.

• popodnevni sastanak = an afternoon meeting
• sastanak popodne = a meeting in the afternoon or the meeting is in the afternoon, depending on context

So:

• popodnevni describes the noun directly as an adjective
• popodne gives the time more like an adverbial expression

Examples:

• Imamo popodnevni sastanak. = We have an afternoon meeting.
• Imamo sastanak popodne. = We have a meeting in the afternoon.

In your sentence, popodnevni sastanak is the more compact noun phrase.