Vår avgång är klockan nio, men vi måste göra ett byte i centrum.

Because avgång is a common-gender noun in Swedish (an en-word: en avgång).
Possessives agree with the gender and number of the noun:

• vår
  • en-word singular
• vårt
  • ett-word singular
• våra
  • plural

So:

• vår avgång = our departure
• but vårt hus = our house
• and våra biljetter = our tickets

In Swedish, when a noun has a possessive like min, din, vår, deras, you normally do not use a separate article.

So Swedish says:

• vår avgång = our departure

not something like den vår avgång.

This is similar to English, where we say our departure, not the our departure.

Avgång is a noun meaning departure. In travel contexts, it refers to the time a train, bus, flight, or ferry leaves.

Examples:

• tågets avgång = the train’s departure
• nästa avgång = the next departure

Be aware that avgång can also mean resignation or leaving office in other contexts, so the meaning depends on the situation.

Swedish often uses a structure like:

• Avgången är klockan nio
  literally: The departure is at nine o’clock

This is a normal way to express scheduled times. English often prefers Our departure is at nine or We leave at nine. Swedish can also use a verb in some contexts, but är klockan nio is very natural when talking about a scheduled departure time.

In time expressions, Swedish often uses klockan before the hour:

• klockan nio = at nine o’clock
• klockan tre = at three o’clock

Literally, klockan means the clock, but in this expression it just functions as part of telling time.

So:

• är klockan nio = is at nine o’clock

You do not need an extra word meaning at here.

Because Swedish usually does not use a separate preposition like English at in this kind of time expression.

Compare:

• English: at nine
• Swedish: klockan nio

So Vår avgång är klockan nio is the normal Swedish way to say it.

After modal verbs like måste (must), Swedish uses the infinitive without att.

So:

• vi måste göra = we must do
• jag kan komma = I can come
• du vill läsa = you want to read

This is similar to English, where we say must do, not must to do.

Both ideas exist in Swedish, but göra ett byte is a common way to talk about making a transfer or changing from one vehicle to another.

• göra ett byte = make a transfer / make a change
• byta = change / switch

In travel language, you may hear both:

• Vi måste göra ett byte i centrum
• Vi måste byta i centrum

The first focuses on the transfer as a noun (ett byte), while the second uses the verb byta directly. Both are natural.

Here ett byte means a transfer or a change, usually between buses, trains, metro lines, and so on.

For example:

• ett byte = one transfer
• två byten = two transfers

This is a neuter noun, which is why it uses ett:

• ett byte

Do not confuse it with other meanings of byte, which can also mean exchange or even prey in completely different contexts.

Because i is the normal preposition for being in or in the area of the city center:

• i centrum = in the center / downtown

Swedish usually says:

• bo i centrum = live downtown
• träffas i centrum = meet in the center

Using på would generally sound wrong here.

Centrum is often used in Swedish as a kind of fixed place expression, especially when talking about a town or city center.

So:

• i centrum = in the city center / downtown

You do not need to say something equivalent to in the center with a separate article the way English does. Swedish often leaves it as just centrum in this expression.

No, men (but) does not create subordinate-clause word order. It joins two main clauses, so normal main-clause word order stays in place.

That is why you get:

• Vår avgång är klockan nio
• men vi måste göra ett byte i centrum

In Swedish main clauses, the finite verb normally comes in the second position (V2 word order). In the second clause, vi is first and måste is second, which is exactly what we expect.

Yes, depending on context. Avgång is perfectly normal, especially in travel and scheduling, but in everyday speech people might also say things like:

• Vi åker klockan nio = We leave/go at nine
• Tåget går klockan nio = The train leaves at nine

So avgång sounds slightly more tied to schedules, announcements, timetables, or travel planning.

The original sentence is correct and natural, but in everyday conversation many speakers might simplify it a bit, for example:

• Vi åker klockan nio, men vi måste byta i centrum.

This is a little more direct and conversational:

• vi åker = we leave/go
• måste byta = must change / transfer

The original version is still good Swedish; it just sounds a bit more formal or timetable-like because of avgång and göra ett byte.