I programbladet står der, at forestillingen er to timer lang uden pause.

Because Danish often puts a time/place phrase first when it sets the scene.

I programbladet means in the programme / in the playbill.
So the sentence starts by telling you where the information is found.

A very neutral version would be:

Der står i programbladet, at ...

But Danish can move i programbladet to the front for emphasis or just for natural variation:

I programbladet står der, at ...

Both are correct.

Because programbladet is the definite form: the programme.

The noun is:

• et programblad = a programme
• programbladet = the programme

In Danish, definiteness is often shown by adding an ending to the noun instead of using a separate word like the.

Since this sentence refers to the specific programme for the event, Danish uses programbladet.

Yes, literally står means stands, but Danish often uses stå for written information.

So:

• Der står, at ... = It says that ...
• literally: It stands written that ...

This is very common in Danish. English usually says it says or it says in the programme, while Danish often says it stands in that context.

Here der is part of the common expression der står ..., meaning it says ... / there is written ...

A useful way to think of it is:

• Der står i programbladet, at ... = It says in the programme that ...

When I programbladet is moved to the front, Danish main-clause word order changes, so you get:

• I programbladet står der, at ...

So der is still there, but now it comes after the verb.

It does not mean a literal physical there in the same way English always uses it.

Because Danish main clauses follow the V2 rule: the finite verb must be in the second position.

So if you put I programbladet first, the verb must come next:

• I programbladet = first element
• står = second element

Then the rest follows:

• der, at forestillingen ...

That is why står must come before der here.

At means that and introduces a subordinate clause.

So:

• står der, at forestillingen er ...
• it says that the performance is ...

Everything after at is the content of what the programme says.

Because forestillingen means the performance / the show, in the definite singular form.

The noun is:

• en forestilling = a performance / a show
• forestillingen = the performance / the show

Again, Danish usually marks definiteness with an ending:

• -en for many common-gender nouns
• -et for many neuter nouns

So forestillingen is the performance.

Because after at, you are in a subordinate clause, and Danish subordinate clauses normally have subject + verb order.

So:

• at forestillingen er to timer lang

This is normal subordinate-clause order.

Compare:

• Main clause: I programbladet står der ...
  Here Danish uses V2 word order.
• Subordinate clause: at forestillingen er ...
  Here the subject comes before the verb.

That difference is very important in Danish grammar.

Because lang agrees with forestillingen, and forestilling is a common-gender noun.

So:

• en forestilling
• forestillingen er lang
• forestillingen er to timer lang

If the noun were neuter, you would use langt instead:

• et stykke
• stykket er to timer langt

So in your sentence, lang is correct because it describes forestillingen.

This is a normal Danish way to express duration with nouns like film, forestilling, koncert, and so on.

Literally it is:

• two hours long

So:

• forestillingen er to timer lang = the performance is two hours long

Danish often uses lang in exactly this way for the length or duration of an event.

Because Danish uses the plural after numbers greater than one.

So:

• en time = one hour
• to timer = two hours

That is why the sentence has to timer.

Because Danish often leaves out the article in fixed, general expressions like this.

So:

• uden pause = without a break / without an intermission

This sounds natural and general.

Using uden en pause is possible in some contexts, but it sounds more like you are thinking about one specific pause as a separate concrete thing. In this sentence, uden pause is the normal choice.

In this context, pause usually means an intermission / interval in a performance.

So to timer lang uden pause means the performance lasts two hours and there is no break in the middle.

Yes. A very common alternative would be:

I programbladet står der, at forestillingen varer to timer uden pause.

Here varer means lasts.

Both are natural, but they are slightly different in structure:

• er to timer lang = is two hours long
• varer to timer = lasts two hours

Both mean essentially the same thing in this context.