Tegen de tijd dat wij dit vastleggen, is alles duidelijk.

It means by the time (that).

So:

• Tegen de tijd dat wij dit vastleggen = By the time we finalize/record this

This is a very common Dutch time expression. English often leaves out that here, but Dutch normally keeps dat in this structure.

Because dat introduces the clause that follows de tijd.

So Dutch builds it like this:

• tegen de tijd dat ...
• literally: toward/by the time that ...

In English, by the time we... often sounds natural without that, but in Dutch tegen de tijd dat is the standard pattern.

Because after dat, Dutch uses subordinate clause word order, where the conjugated verb goes to the end.

Compare:

• Main clause: Wij leggen dit vast.
• Subordinate clause: dat wij dit vastleggen

So in the sentence:

• dat wij dit vastleggen

the verb is placed at the end because dat creates a subordinate clause.

Good question. Vastleggen is a separable verb.

In a normal main clause, it splits:

• Wij leggen dit vast.

But in subordinate clauses and infinitives, it usually stays together:

• dat wij dit vastleggen
• om dit vast te leggen

So here it is one word because it is inside a dat-clause.

Vastleggen can mean several related things, depending on context:

• to record
• to write down
• to establish
• to fix formally
• to finalize

In this sentence, it probably means something like:

• to formally record/finalize this
• to put this on record
• to set this down clearly

So the idea is that everything will already be clear by the moment it is officially written down or established.

Dutch often uses the present tense where English might naturally use will.

So Dutch says:

• Tegen de tijd dat wij dit vastleggen, is alles duidelijk.

Even though in English you might translate it as:

• By the time we finalize this, everything will be clear.

That is normal Dutch usage. The future meaning is understood from the time expression, so zullen is often unnecessary.

Because the sentence begins with an adverbial element:

• Tegen de tijd dat wij dit vastleggen

In Dutch main clauses, the finite verb normally comes in second position. If something other than the subject comes first, the verb comes before the subject.

So:

• Normal order: Alles is duidelijk.
• After a fronted time phrase: Tegen de tijd dat wij dit vastleggen, is alles duidelijk.

This is called inversion.

Both wij and we mean we.

• we is more common in everyday speech
• wij can sound a bit more careful, formal, or emphatic

In writing, especially slightly formal or neutral writing, wij is very normal.

So:

• wij dit vastleggen and we dit vastleggen are both possible

The comma separates the opening time expression from the main clause:

• Tegen de tijd dat wij dit vastleggen, is alles duidelijk.

This is very common in Dutch when a longer subordinate or adverbial clause comes first. It helps readability.

Because alles is grammatically treated as singular in Dutch.

So you say:

• Alles is duidelijk.

not:

• Alles zijn duidelijk.

Even though everything refers to many things in meaning, the word itself takes a singular verb.

You could, but it does not mean exactly the same thing.

• Tegen de tijd dat wij dit vastleggen = by the time we finalize this
• Als wij dit vastleggen = if/when we finalize this

The original sentence focuses on time and suggests that clarity will already have been reached by that point.
Using als makes it sound more like a condition or simple event, not specifically by that time.

The core main clause is:

• Alles is duidelijk.
  = Everything is clear.

Then Dutch adds the time phrase in front:

• Tegen de tijd dat wij dit vastleggen, is alles duidelijk.

This is useful to remember because it helps you see why the word order changes in the main clause.