Kroz probno razdoblje provjeravajte brzinu interneta.

Here kroz means something like throughout or during.

Its basic literal meaning is through, as in moving through space, but it is also often used with time expressions to mean over the course of a period.

So kroz probno razdoblje means throughout the trial period.

A very common alternative in Croatian would be tijekom probnog razdoblja, which is often a bit more natural in formal writing.

Because kroz takes the accusative case.

• dictionary form: probno razdoblje
• accusative singular: probno razdoblje

For this neuter noun, the accusative singular looks the same as the nominative, so nothing changes on the surface.

Compare:

• kroz probno razdoblje = accusative, after kroz
• tijekom probnog razdoblja = genitive, after tijekom

So the form is correct because the preposition determines the case.

Provjeravajte is the imperative form of the imperfective verb provjeravati.

It means:

• check repeatedly
• keep checking
• be checking from time to time

This is a very natural choice here because the sentence is talking about something done over a period of time, not just once.

It is also the form used for:

• you all check
• polite singular you check

So it can address either multiple people or one person formally.

Because Croatian often uses aspect very clearly.

• provjeravati = imperfective = ongoing, repeated, habitual
• provjeriti = perfective = completed, one-time check

Since the sentence refers to doing this throughout a trial period, the imperfective imperative provjeravajte fits better: it suggests repeated monitoring.

If you used a perfective form, it would sound more like check it once or make a check, which does not match the idea of an entire trial period as well.

Because brzinu is the accusative singular of brzina.

• nominative: brzina = speed
• accusative: brzinu

Here brzinu interneta is the direct object of the verb provjeravajte, so it must be in the accusative.

So:

• brzina = subject form
• brzinu = object form

Because Croatian expresses the speed of the internet with a genitive construction:

• brzina interneta = internet speed / the speed of the internet

Here:

• brzinu is accusative because it is the direct object
• interneta is genitive because it depends on brzina

This is very common in Croatian:

• cijena proizvoda = the price of the product
• boja auta = the color of the car
• brzina interneta = the speed of the internet

No, Croatian word order is fairly flexible.

This sentence is perfectly fine:

• Kroz probno razdoblje provjeravajte brzinu interneta.

But you could also say:

• Provjeravajte brzinu interneta kroz probno razdoblje.

The first version puts the time phrase first, which gives it a slight emphasis, like setting the scene: throughout the trial period...

In instructions, both are possible. Croatian often moves elements around for focus rather than strict grammatical necessity.

In many contexts, yes.

• kroz probno razdoblje is understandable and grammatical
• tijekom probnog razdoblja often sounds more formal and more natural in written instructions

So you may often see:

• Tijekom probnog razdoblja provjeravajte brzinu interneta.

The main difference is grammatical too:

• kroz
  • accusative → kroz probno razdoblje
• tijekom
  • genitive → tijekom probnog razdoblja

Both can mean roughly during the trial period, but tijekom is especially common for time periods in standard written Croatian.

It can be either:

• more than one person
• one person politely/formally

That is because provjeravajte is the 2nd person plural imperative, and Croatian uses that form both for:

• plural you
• polite singular you

So without more context, the sentence could be:

• an instruction to several users
• a formal instruction to one customer

Yes, very much so.

The wording sounds like a recommendation or instruction you might see in:

• a user guide
• a telecom provider message
• a website explaining a free trial or testing period
• technical advice

The imperative provjeravajte gives it an instructional tone, similar to English phrases like:

• Monitor your internet speed during the trial period
• Keep checking your internet speed throughout the trial period

So grammatically and stylistically, it fits an instructional context well.