He de mirar l'hora abans de sortir de casa.

Here he is the first-person singular form of the verb haver in the structure haver de + infinitive, which expresses obligation or necessity.

So:

• he de mirar = I have to look / I must check
• has de mirar = you have to look
• ha de mirar = he/she has to look

This is a very common Catalan pattern:

• He de marxar. = I have to leave.
• Hem d'estudiar. = We have to study.

So in this sentence, he de means I have to, not the English pronoun he.

Catalan often omits subject pronouns when the verb ending already makes the subject clear.

• He de mirar... already tells you the subject is I
• Adding jo is possible, but usually unnecessary:
  • Jo he de mirar l'hora...

Using jo would usually add emphasis or contrast, for example:

• Jo he de mirar l'hora, però tu no.
  I have to check the time, but you don’t.

So the version without jo is the most natural neutral form.

Yes, literally it is something like look at the time/hour, but in natural English it usually means check the time.

In Catalan, mirar often means:

• to look at
• to check
• to see/look up

So mirar l'hora is the normal way to say check the time.

Other examples:

• Mira el mòbil. = Check the phone / Look at the phone.
• He de mirar el tren. = I have to check the train schedule (depending on context)

So even though the literal wording may sound slightly different from English, it is a normal Catalan expression.

Because la becomes l' before a word beginning with a vowel or silent h.

So:

• la hora → l'hora
• la amiga → l'amiga
• el home → l'home

This is just the normal apostrophe/elision rule in Catalan.

So l'hora means the time / the hour.

Because the fixed pattern is:

• abans de + infinitive = before doing something

So:

• abans de sortir = before leaving / before going out
• abans de menjar = before eating
• abans d'arribar = before arriving

If a noun follows instead of an infinitive, you can also use abans de:

• abans de classe = before class

This de is required in the structure.

Because sortir normally uses de to mean go out of / leave from a place.

So:

• sortir de casa = leave home
• sortir de l'oficina = leave the office
• sortir del cotxe = get out of the car

Without de, it would be ungrammatical here.

In Catalan, casa without an article often means home in a general, familiar sense.

So:

• sortir de casa = leave home
• ser a casa = be at home
• tornar a casa = go back home

But la casa usually refers more specifically to the house/building itself.

Compare:

• Surto de casa. = I’m leaving home.
• Surto de la casa blanca del final del carrer. = I’m leaving the white house at the end of the street.

So de casa is idiomatic when you mean home.

In this sentence, leave is usually the best English translation:

• abans de sortir de casa = before leaving home

But sortir can also mean go out, depending on context.

Examples:

• Surto de casa a les vuit. = I leave home at eight.
• Vull sortir aquesta nit. = I want to go out tonight.

So the core idea of sortir is to go out / to leave, and the context tells you which English wording sounds most natural.

The sentence follows a very normal Catalan order:

• He de mirar l'hora = I have to check the time
• abans de sortir de casa = before leaving home

So the structure is:

• verb phrase
  • object
    • time-related phrase

A simple breakdown is:

• He de mirar → I have to check
• l'hora → the time
• abans de sortir de casa → before leaving home

Catalan word order here is very close to English, which makes this sentence relatively straightforward once you understand the grammar points above.