Tegen de tijd dat de proefperiode eindigt, zijn de werktijden vastgelegd.

Tegen de tijd dat is a fixed expression meaning by the time (that).

It introduces a time clause and suggests that something in the main clause will be true or completed no later than that moment.

So in this sentence, it means that when the probation period ends, the working hours will already have been fixed.

Because dat introduces a subordinate clause.

In Dutch subordinate clauses, the finite verb usually goes to the end. So:

• de proefperiode eindigt = main clause word order
• dat de proefperiode eindigt = subordinate clause word order

That is why eindigt comes last.

This is because Dutch main clauses follow the V2 rule: the finite verb must come in the second position.

Here, the whole time phrase Tegen de tijd dat de proefperiode eindigt comes first. After that, the finite verb must come immediately:

• Tegen de tijd dat de proefperiode eindigt, zijn de werktijden vastgelegd.

So the order is:

1. first element: Tegen de tijd dat de proefperiode eindigt
2. finite verb: zijn
3. subject: de werktijden
4. rest: vastgelegd

If the sentence began with the subject, then you would get:

• De werktijden zijn vastgelegd tegen de tijd dat de proefperiode eindigt.

That is also grammatical, though less natural in many contexts.

Dutch often uses the present tense to talk about the future when the time reference is already clear.

Because tegen de tijd dat clearly points to a future moment, eindigt is understood as future:

• de proefperiode eindigt = the probation period ends / will end

Using zal eindigen is possible in some contexts, but it is often unnecessary and can sound heavier.

Yes, this is a passive/resultative-type construction.

The verb is vastleggen, which means things like:

• to lay down
• to establish
• to fix
• to record formally

So de werktijden zijn vastgelegd means that the working hours have been fixed/established.

In this sentence, the idea is not mainly the process of fixing them, but the result: by that time, they are already set.

A useful contrast:

• De werktijden worden vastgelegd. = the working hours are being fixed / are being established
• De werktijden zijn vastgelegd. = the working hours have been fixed / are set

Dutch often uses the present perfect to express that something will be completed before a future point.

So:

• Tegen de tijd dat de proefperiode eindigt, zijn de werktijden vastgelegd.

means something like:

• By the time the probation period ends, the working hours will have been fixed.

English often uses future perfect here, but Dutch commonly uses the normal perfect form instead, as long as the time reference makes the future meaning clear.

Proefperiode is a compound noun:

• proef = trial / test
• periode = period

Together, proefperiode means trial period or probation period, depending on context.

In work-related contexts, it usually means probation period.

It is a de-word:

• de proefperiode

Werktijden means working hours or work hours.

It is plural because it refers to the actual hours or schedule of work, not just the abstract idea of working time.

Compare:

• werktijd = working time in a more general or abstract sense
• werktijden = concrete working hours, shifts, or schedule

So de werktijden here means the employee’s agreed working hours.

In this sentence, vastgelegd means something like:

• fixed
• set
• laid down
• formally agreed
• recorded

The best English choice depends on context. For working hours, common translations would be:

• the working hours have been fixed
• the working hours have been set
• the working hours have been laid down

The Dutch word often suggests that something has been formally determined or officially recorded.

Not exactly, because the nuance changes.

• als / wanneer = when
• tegen de tijd dat = by the time

Tegen de tijd dat strongly suggests that the main action is completed no later than that point.

Compare:

• Wanneer de proefperiode eindigt, zijn de werktijden vastgelegd.
  = When the probation period ends, the working hours have been fixed.

• Tegen de tijd dat de proefperiode eindigt, zijn de werktijden vastgelegd.
  = By the time the probation period ends, the working hours are already fixed.

So tegen de tijd dat emphasizes completion before that deadline-like moment.