Cuando escucho música, el viaje en autobús se me hace más corto.

Because the sentence describes a habitual situation: whenever I listen to music, the bus journey feels shorter. In Spanish, cuando + present indicative is normal for repeated or general actions.

If you were talking about a future event, Spanish often uses the subjunctive instead:

• Cuando escucho música, me relajo. = whenever I listen to music, I relax
• Cuando escuche música esta tarde, me relajaré. = when I listen to music this afternoon, I will relax

Escucho gives a general or habitual meaning. It fits the idea of when I listen to music in general.

Estoy escuchando música would focus on something happening right now, at this moment. That would not fit as well with the general idea of the sentence.

In Spanish, broad, non-specific nouns often appear without an article after verbs like escuchar, leer, or comprar.

So:

• escuchar música = listen to music in general
• escuchar la música = listen to specific music, or the music that has already been mentioned

Here the meaning is general, so música without an article is the natural choice.

It means the bus journey or the trip by bus.

• viaje = trip, journey
• en autobús = by bus

So the whole phrase refers to the journey taken on the bus.

En autobús means by bus, focusing on the means of transport.

En el autobús means on the bus, which focuses more on being physically inside a particular bus.

Compare:

• Voy al trabajo en autobús. = I go to work by bus
• Estoy en el autobús. = I am on the bus

In your sentence, the idea is the journey by bus in general, so en autobús is right.

Spanish often uses the definite article where English would use a possessive, especially when it is already clear whose thing or experience is being talked about.

So el viaje en autobús naturally means the bus journey I am taking. Adding mi is possible, but not necessary.

Se me hace is an idiomatic expression. Here it means something like:

• it feels to me
• it seems to me
• it becomes, in my perception

So:

El viaje en autobús se me hace más corto
= The bus journey feels shorter to me

This is not something you should translate word for word.

Me shows who experiences the feeling: to me.

The se hace part belongs to the expression. In this structure, the subject is the thing being experienced, and me marks the person affected by that experience.

So:

• el viaje = the journey
• se hace = feels/becomes
• me = to me

Together, se me hace más corto means it feels shorter to me.

The subject is el viaje en autobús.

That is why the verb is singular:

• el viaje ... se me hace
  not
• el viaje ... se me hacen

The journey is the thing that feels shorter.

Because corto agrees with viaje, and viaje is masculine singular.

So the adjective must also be masculine singular:

• el viaje → más corto

If the noun were feminine, the adjective would change:

• la espera se me hace más corta = the wait feels shorter to me

Here it is about perceived duration, not physical distance.

Spanish often uses corto and largo for experiences that feel short or long in time:

• La clase se me hizo corta. = The class felt short
• La reunión se me hizo larga. = The meeting felt long

So in your sentence, the journey feels shorter in time.

Yes. El viaje en autobús me parece más corto is correct and natural.

Both versions are similar, but there is a slight nuance:

• me parece más corto = it seems shorter to me
• se me hace más corto = it feels shorter to me

The version with se me hace often sounds a bit more personal or experiential.

Because the sentence starts with a time clause. In Spanish, when this kind of subordinate clause comes before the main clause, it is normally separated by a comma.

So this is standard:

• Cuando escucho música, el viaje en autobús se me hace más corto.

If you reverse the order, the comma is usually not used:

• El viaje en autobús se me hace más corto cuando escucho música.

It is very common and completely standard in Spain.

In Latin America, other words may also be used, depending on the country, such as:

• bus
• camión
• colectivo
• guagua

But autobús is widely understood.