Confirmamos la hora en que empieza el desmontaje.

Confirmamos is the 1st person plural present indicative of confirmar.

So it means we confirm.

Depending on context, Spanish present tense can also sound like:

• we are confirming
• we confirm
• sometimes a general/business-style we confirm

By itself, it is not the simple past we confirmed. That would normally be confirmamos too in some contexts, but then the surrounding context would make that clear. Spanish has this overlap in the nosotros form:

• present: confirmamos
• preterite: confirmamos

So context tells you which one is meant. In this sentence, the most natural reading is we confirm.

Spanish usually uses the definite article here because it is referring to a specific time:

• la hora = the time

So Confirmamos la hora... is literally We confirm the time...

This is very normal in Spanish. English sometimes drops articles where Spanish keeps them.

Here, en que means something like when or at which.

It connects la hora with the clause that follows:

• la hora en que empieza el desmontaje
• literally: the time at which the dismantling starts

So que is a relative pronoun, and en is the preposition used with it.

A natural English translation is just:

• the time when the dismantling starts

Yes. In fact, a la que is very common here, and many learners will hear it more often with hora.

So these are both possible:

• la hora en que empieza el desmontaje
• la hora a la que empieza el desmontaje

Why a la que? Because with clock times, Spanish often uses a:

• empieza a las ocho

That is why a la que can feel especially logical with hora.

Very roughly:

• en que can sound a bit more neutral or formal/written
• a la que is also very standard and often very natural in speech

Because this clause is treated as factual / definite, not uncertain or hypothetical.

The sentence refers to a specific event:

• there is a dismantling
• it has a start time
• we are confirming that time

So Spanish uses the indicative:

• empieza

The subjunctive empiece would usually appear if the time were unknown, not yet identified, or part of a more hypothetical idea.

Compare:

• Confirmamos la hora en que empieza el desmontaje.
  We are talking about the actual time it starts.

• Buscamos una hora en que empiece el desmontaje.
  This could sound more like we are looking for a suitable time for it to start.

Because Spanish often uses the present tense for scheduled or expected future events.

This is very common with timetables, plans, events, and arrangements.

So:

• empieza can mean starts
• in context, that may refer to something happening later

English does something similar:

• The meeting starts at 9.
• Our flight leaves tomorrow.

So empieza here is perfectly natural even if the dismantling has not started yet.

Desmontaje is a noun meaning dismantling, taking apart, or takedown.

It comes from the verb desmontar = to dismantle / take apart / take down.

In Spain, desmontaje is very common in contexts like:

• events
• fairs
• exhibitions
• stages
• technical setups
• equipment

For example, after an event:

• montaje = setup
• desmontaje = takedown

So in this sentence, it likely refers to the moment when the takedown or dismantling process begins.

Because Spanish often uses the article with nouns where English might not.

Here, el desmontaje refers to a specific dismantling process:

• the dismantling
• the takedown

So:

• empieza el desmontaje = the dismantling starts

Leaving out the article would sound unnatural in this sentence.

Also, desmontaje is a masculine noun, so it takes el.

Yes, absolutely. That is a very natural alternative.

Compare:

• Confirmamos la hora en que empieza el desmontaje.
  We confirm the time when the dismantling starts.

• Confirmamos a qué hora empieza el desmontaje.
  We confirm what time the dismantling starts.

The second version often feels a bit more direct and conversational, because a qué hora is the standard way to say at what time.

So both are correct, but:

• la hora en que... sounds slightly more formal or structured
• a qué hora... often sounds more everyday and natural

Not naturally in this sentence.

Spanish normally prefers:

• la hora en que...
• la hora a la que...

After a noun like hora, using cuando is generally not the standard choice here.

So:

• la hora en que empieza el desmontaje = good
• la hora a la que empieza el desmontaje = good
• la hora cuando empieza el desmontaje = usually not recommended

But cuando works perfectly if you remove la hora:

• Confirmamos cuándo empieza el desmontaje.
  We confirm when the dismantling starts.

So the difference is:

• with a noun like la hora, use en que / a la que
• without that noun, cuándo works very well