Kad budemo imali više vremena, pogledat ćemo novu izložbu u galeriji.

Because after kad when talking about a future time, Croatian often uses Future II in the subordinate clause, not ordinary Future I.

So:

• kad budemo imali više vremena = when we have / when we will have more time
• main clause: pogledat ćemo... = ordinary Future I

This is very common with conjunctions like kad, ako, čim, and similar words introducing future conditions or time frames.

A very literal English-style kad ćemo imati would usually sound unnatural here.

It is Future II.

Future II is formed with:

• the present tense of biti in the budem set:
  • budem, budeš, bude, budemo, budete, budu
• plus the past active participle of the main verb

Here:

• budemo = we will / we shall in the Future II pattern
• imali = participle of imati (to have)

So:

• budemo imali = we will have / when we have

Even though it contains a participle, you should think of it as a normal future verb form, not as a separate be + had structure like in English.

The form of the participle agrees with the subject.

The subject is not written, but it is understood as mi = we.

• imali = masculine plural or mixed-gender plural
• imale = feminine plural

So if the speakers are:

• a mixed group, or at least one male: kad budemo imali
• an all-female group: kad budemo imale

Textbooks often give the masculine/mixed form as the default.

In standard Croatian, when the future auxiliary comes after the infinitive, the final -i of the infinitive is dropped in writing.

So:

• pogledati + ćemo → pogledat ćemo

This is the normal written form.

You can also say:

• ćemo pogledati

That version keeps the full infinitive because the auxiliary comes first.

So both are correct:

• pogledat ćemo novu izložbu
• ćemo pogledati novu izložbu

But pogledati ćemo is not the standard written form.

Because pogledati is a perfective verb, and it fits a single completed future action well.

• pogledati = to look at / see / view once, as a complete event
• gledati = to watch / be looking / do the action in an ongoing or repeated way

Here the idea is:

• we’ll go and see the new exhibition

That is naturally expressed with pogledati.

If you used gledati, it would suggest a more ongoing process and would sound less natural for visiting an exhibition once.

Because izložbu is the direct object of pogledat ćemo, so it is in the accusative case.

The dictionary form is:

• izložba = exhibition

Accusative singular becomes:

• izložbu

And the adjective must match it:

• nova izložba → nominative
• novu izložbu → accusative

So:

• pogledat ćemo novu izložbu = we’ll see the new exhibition

Because u galeriji means in the gallery, describing location, not movement.

Croatian uses:

• u + locative for being in a place
• u + accusative for moving into a place

So:

• u galeriji = in the gallery
• u galeriju = into the gallery

In this sentence, the exhibition is located there, so u galeriji is correct.

Because after quantity words like više (more), Croatian usually uses the genitive.

The noun is:

• vrijeme = time

After više, it becomes:

• vremena

So:

• više vremena = more time

This is a very common pattern:

• više novca = more money
• više vode = more water
• više knjiga = more books

Croatian often leaves subject pronouns out because the verb ending already shows the person and number.

Here both verbs show we:

• budemo = we
• ćemo = we will

So mi is not necessary.

You can add it for emphasis:

• Kad mi budemo imali više vremena, pogledat ćemo novu izložbu u galeriji.

But in normal neutral speech, leaving mi out sounds more natural.

Because the sentence begins with a subordinate clause:

• Kad budemo imali više vremena, ...

When that clause comes first, Croatian normally separates it from the main clause with a comma.

So:

• Kad budemo imali više vremena, pogledat ćemo novu izložbu u galeriji.

If you reverse the order, you usually do not need the comma:

• Pogledat ćemo novu izložbu u galeriji kad budemo imali više vremena.

Yes. Croatian word order is fairly flexible, although some versions sound more neutral than others.

Neutral order:

• Kad budemo imali više vremena, pogledat ćemo novu izložbu u galeriji.

Also possible:

• Pogledat ćemo novu izložbu u galeriji kad budemo imali više vremena.
• Novu izložbu u galeriji pogledat ćemo kad budemo imali više vremena.

Changing the order usually changes focus or emphasis, not the basic meaning.

The original sentence is a very natural, standard way to say it.