Em desperto aviat quan treballo a l'oficina.

Because despertar-se is the usual verb for to wake up in Catalan.

• Em desperto = I wake up
• Literally, it is reflexive: I wake myself

Without the reflexive pronoun, despertar is often transitive:

• Desperto el nen = I wake the child

So for a learner, the safest rule is:

• despertar-se = to wake up
• despertar = to wake someone/something

Catalan object and reflexive pronouns usually go before a conjugated verb:

• Em desperto
• Em llevo
• Em dutxo

It is em here because the next word starts with a consonant sound: desperto.

Before a vowel or silent h, it usually becomes m':

• M'aixeco
• M'he despertat

So:

• em
  • consonant
• m'
  • vowel or silent h

Catalan often leaves out subject pronouns because the verb ending already tells you who the subject is.

• desperto = I wake up
• treballo = I work

The ending -o already shows first person singular, so jo is not necessary.

You can add jo for emphasis or contrast:

• Jo em desperto aviat, però ell no.

But in a normal sentence, leaving it out is more natural.

Both are first person singular, present indicative.

• despertar-se → em desperto
• treballar → treballo

So the sentence is using the present tense to talk about a habit or a repeated situation.

In other words, it means something like:

• I wake up early when I work at the office
• or Whenever I work at the office, I wake up early

This is a very good question, because aviat can be tricky.

Very often, aviat means soon.
When talking about doing something early in the day, many speakers would more naturally say d'hora.

So a very natural version would be:

• Em desperto d'hora quan treballo a l'oficina.

That said, aviat can still be understood in some contexts as early, especially depending on region or context. But as a learner, it is useful to know:

• aviat often = soon
• d'hora often = early

Grammatically, quan means when, but in a sentence like this it often has the broader sense of whenever.

Because the whole sentence describes a habit, the meaning is not usually one specific occasion. It means something like:

• When/whenever I work at the office, I wake up early

So quan here introduces the situation in which the main action happens.

Because oficina is a feminine noun, and the article la becomes l' before a vowel:

• la oficina → l'oficina

After the preposition a, you get:

• a l'oficina

So this means at the office or in the office.

The apostrophe is just showing that the vowel of the article has dropped before another vowel.

It can correspond to either one in English.

Catalan often uses a in places where English might choose at or in, depending on context.

So:

• treballo a l'oficina can be translated as
  • I work at the office
  • I work in the office

In this sentence, at the office is probably the most natural English translation, but both are possible depending on style.

Yes, but the meaning changes slightly.

• despertar-se = to wake up
• llevar-se = to get up / get out of bed

So:

• Em desperto d'hora focuses on the moment you wake up
• Em llevo d'hora focuses on getting out of bed

In everyday speech, English often uses get up early, so em llevo d'hora is also very common. But if you specifically mean wake up, then em desperto is the better match.

Yes. You can also say:

• Quan treballo a l'oficina, em desperto aviat.

That word order is completely normal. The meaning stays the same.

A rough difference in feel is:

• Em desperto aviat quan treballo a l'oficina = starts with the main action
• Quan treballo a l'oficina, em desperto aviat = starts with the time/condition

If the quan clause comes first, it is also very common to write a comma after it.