Det tager kun to minutter at købe boller, når der ikke er nogen kø.

Det is an impersonal subject here. Danish often uses det in expressions where English uses it, even though det does not refer to a specific thing.

So det tager ... means it takes ...

Examples:

• Det tager en time. = It takes an hour.
• Det tager kun to minutter. = It only takes two minutes.

In this sentence, det is not standing for a noun like the trip or the task. It is just the normal way to form this kind of expression in Danish.

Tager is the present tense of tage.

• tage = to take
• tager = takes / is taking

Because the sentence is stating a general fact, Danish uses the present tense:

• Det tager kun to minutter ... = It takes only two minutes ...

If you used tage, that would be the infinitive form, which would not work as the main verb here.

Kun means only, and in this sentence it modifies the time expression to minutter.

So:

• kun to minutter = only two minutes

This placement is very natural in Danish. English does the same thing:

• It takes only two minutes

You could think of kun as narrowing the amount of time.

After expressions like det tager ..., Danish usually uses an infinitive with at to say what action takes that amount of time.

So:

• Det tager to minutter at købe boller.
• literally: It takes two minutes to buy rolls/buns.

Here:

• at = infinitive marker, like English to
• købe = buy

This structure is very common:

• Det er svært at forstå. = It is hard to understand.
• Det tager lang tid at lære dansk. = It takes a long time to learn Danish.

Because boller is being used in a general, indefinite way.

• købe boller = buy rolls / buns
• købe nogle boller = buy some rolls / buns
• købe bollerne = buy the rolls / buns

In this sentence, the speaker is talking about the activity in general, not specific buns. Danish often leaves out an article or determiner in this kind of general object phrase, especially after verbs like købe, spise, drikke, and so on.

So at købe boller sounds natural as a general activity.

Boller is the plural of bolle.

In everyday Danish, boller usually means bread rolls or buns, depending on context.

So in a sentence about buying them quickly and mentioning a queue, many learners would understand it as something like buying bread rolls from a bakery or shop.

This is a very common question.

• når is often used for something that happens when a situation occurs, especially if it is seen as real, typical, or repeated.
• hvis means if and is more clearly conditional or hypothetical.

Here, the sentence describes a general situation:

• It only takes two minutes to buy buns when there is no queue.

So når der ikke er nogen kø means something like:

• when there isn’t a queue
• whenever there isn’t a queue

If you used hvis, it would sound more like a pure condition:

• if there is no queue

That is possible in some contexts, but når fits very naturally when talking about a normal repeated situation.

Because der er is the normal Danish structure for there is / there are.

So:

• der er en kø = there is a queue
• der er ikke nogen kø = there isn’t any queue

Here, der is not the same as English there in the sense of a place. It is an existential der, used to say that something exists or does not exist.

You cannot normally replace this der with det.

Because this is a subordinate clause introduced by når.

In Danish subordinate clauses, sentence adverbs like ikke usually come before the finite verb.

So:

• når der ikke er nogen kø

Compare that with a main clause:

• Der er ikke nogen kø.

This difference in word order is very important in Danish.

A useful contrast:

Main clause:

• Der er ikke nogen kø.

Subordinate clause:

• ... når der ikke er nogen kø.

So the position of ikke is one of the clues that you are in a subordinate clause.

Both are possible, but they work slightly differently.

• ikke nogen kø = not any queue
• ingen kø = no queue

So these are both natural:

• der ikke er nogen kø
• der ingen kø er is not natural in modern Danish word order
• der er ingen kø = there is no queue

In your sentence, ikke ... nogen is a standard negative pattern:

• ikke nogen problemer = not any problems
• ikke nogen tid = not any time
• ikke nogen kø = not any queue

Nogen often appears in negative sentences and means something like any.

Because the phrase is indefinite and appears in an existential construction.

• der er en kø = there is a queue
• der er ikke nogen kø = there isn’t any queue

Here, nogen already plays the role of an indefinite determiner, so you do not add en.

You would not say:

• der ikke er nogen en kø

That would be wrong.

It is singular.

• en kø = a queue
• køen = the queue
• køer = queues

In the sentence, kø is singular because it refers to the general existence of a queue:

• there isn’t any queue

A useful breakdown is:

• Det tager kun to minutter = main clause
• at købe boller = infinitive phrase explaining what takes two minutes
• når der ikke er nogen kø = subordinate clause giving the condition/situation

So the overall pattern is:

Det tager + time expression + at + infinitive + når-clause

For example:

• Det tager fem minutter at gå derhen, når vejret er godt.
• Det tager ikke lang tid at lave kaffe, når man har en maskine.

This is a very common and useful Danish sentence pattern.