Wij leggen de arbeidsduur en de kernuren vast.

Because vastleggen is a separable verb in Dutch.

• The full verb is vastleggen, which often means to fix, to determine, to lay down, or to specify.
• In a main clause, Dutch usually puts the conjugated verb in second position.
• With separable verbs, the main verb splits:
  • leggen goes to the normal verb position
  • vast moves to the end

So:

• Wij leggen ... vast. = We set/fix ...
• In the infinitive, it stays together: vastleggen
• In a subordinate clause, it also stays together more often at the end:
  ... dat wij de arbeidsduur en de kernuren vastleggen.

On its own, leggen often does mean to lay, to put, or to place.

But here it is part of the separable verb vastleggen, which has a more abstract meaning. In this sentence, vastleggen means something like:

• to determine
• to fix
• to establish
• to specify
• to formally set down

So you should not interpret leggen by itself here. The meaning comes from the whole verb vastleggen.

Both wij and we mean we.

The difference is mostly about stress and style:

• we is the unstressed, very common spoken form
• wij is the stressed or more emphatic form, and it also appears often in more formal writing

So:

• We leggen de arbeidsduur en de kernuren vast.
• Wij leggen de arbeidsduur en de kernuren vast.

Both are correct.
Using wij can sound a little more formal, clear, or emphatic.

Because the subject is wij (we), which is plural.

The present tense of leggen is:

• ik leg
• jij legt
• u legt
• hij/zij legt
• wij leggen
• jullie leggen
• zij leggen

So wij leggen is the correct form.

Arbeidsduur is a compound noun, which is very common in Dutch.

It is made of:

• arbeid = work / labour
• duur = duration

Together, arbeidsduur means working time, duration of work, or length of the working period, depending on context.

Dutch often forms long nouns this way, just like English can do with words such as workday, bathroom, or schoolbook.

Kernuren is also a compound noun:

• kern = core
• uren = hours

So kernuren literally means core hours.

In work contexts, this usually refers to the hours during which everyone is expected to be present or available, even if people otherwise have flexible schedules.

So it is not just any hours in general; it usually has a specific HR or workplace meaning.

Because both nouns are being presented as definite nouns:

• de arbeidsduur = the working hours / the duration of work
• de kernuren = the core hours

Repeating de is very normal and natural here. It makes it clear that the sentence refers to both specific things.

In some coordinated phrases, Dutch can sometimes omit a repeated article, but here repeating de sounds clear and standard:

• de arbeidsduur en de kernuren

Also, both nouns take the article de, not het.

There is no single perfect rule, but here are the useful points:

• duur is a de-word, so arbeidsduur is also a de-word
• uren is the plural of uur
• All plural nouns in Dutch take de, so de uren
• Therefore: de kernuren

So in this sentence, both nouns correctly use de.

Yes, it is completely normal Dutch main-clause word order.

The pattern is:

• Wij = subject
• leggen = conjugated verb in second position
• de arbeidsduur en de kernuren = direct object
• vast = separated particle at the end

So the structure is:

Subject + finite verb + object + separable particle

That is a very common Dutch pattern with separable verbs.

Yes, absolutely.

That version is probably even more common in everyday speech. The meaning is the same.

• Wij leggen de arbeidsduur en de kernuren vast.
• We leggen de arbeidsduur en de kernuren vast.

The first may feel slightly more formal or emphatic; the second feels more everyday and conversational.

They are related, but not always exactly the same in tone or usage.

• werktijd often means working time in a general, everyday sense
• arbeidsduur can sound a bit more formal, administrative, legal, or HR-related

In a sentence about contracts, policies, or formal agreements, arbeidsduur fits very well.
So even if the meanings overlap, arbeidsduur may sound more official than werktijd.

The dictionary form is vastleggen.

That is the form you would look up in a dictionary, not leggen by itself if you want the meaning used here.

So:

• sentence form: wij leggen ... vast
• dictionary form: vastleggen

This is important with Dutch separable verbs, because the meaning often changes a lot when a particle is added.

No. Vastleggen is quite broad and is used in many contexts.

It can mean:

• to determine formally
• to record
• to set down
• to establish
• to define

For example, it can be used for:

• rules
• agreements
• conditions
• working hours
• procedures
• details in a contract
• even capturing something in an image: een moment vastleggen = to capture a moment

So in this sentence it means something like formally setting or specifying the working duration and the core hours.