A terv szerint holnap korán indulunk.

It means according to the plan or as planned.

• terv = plan
• szerint = according to, in accordance with
• a = the

So a terv szerint is literally according to the plan.

Because szerint is a postposition. In Hungarian, many words that correspond to English prepositions come after the noun phrase, not before it.

So:

• English: according to the plan
• Hungarian: a terv szerint

This is a very common pattern in Hungarian.

A is the definite article, meaning the.

In a terv szerint, it suggests a specific plan that the speakers already know about: the plan.

There is also terv szerint without the article, which often sounds more general or idiomatic, closer to as planned or according to plan.
So the version with a can feel a bit more like referring to a particular plan or schedule.

No. Holnap already means tomorrow, so it works by itself as a time adverb.

Hungarian has many time words like this that do not need extra endings in basic use:

• ma = today
• holnap = tomorrow
• tegnap = yesterday

So holnap on its own is completely normal.

Korán is the adverb meaning early.

• korai = early as an adjective
• korán = early as an adverb

So:

• korai vonat = an early train
• korán indulunk = we leave early

English uses early for both adjective and adverb, but Hungarian uses different forms here.

Indulunk comes from indul, meaning to leave, to depart, to set off, or to start out.

The ending -unk shows:

• 1st person plural
• present tense

So indulunk means we leave, we are leaving, or in the right context we will leave.

Because Hungarian very often uses the present tense for future meaning when the time is already clear.

Here, holnap tells you the action is in the future, so indulunk naturally means we leave / we are leaving tomorrow.

Hungarian can also use a more explicit future form, for example:

• Holnap korán fogunk indulni.

But the simple present is very common and often more natural.

Because Hungarian verbs already show the subject.

The ending -unk in indulunk already means we, so a separate pronoun is usually unnecessary.

If you want emphasis or contrast, you can add mi:

• Mi indulunk holnap, nem ők.
  = We are leaving tomorrow, not they.

But in a normal sentence, leaving out mi is standard.

No, Hungarian word order is fairly flexible. The basic meaning can stay the same, but the emphasis can change.

The given sentence:

• A terv szerint holnap korán indulunk.

sounds natural and neutral.

You could also move things around, for example:

• Holnap korán indulunk a terv szerint.
• Korán indulunk holnap.

These versions may sound slightly different in emphasis or style, but they are still understandable. In Hungarian, word order often shows what is being highlighted, not just grammatical roles.

Yes, but in many situations they are close.

• indulunk = we leave / we set off
• elindulunk = we set off / we start out, often with a stronger sense of the action beginning

The prefix el- can make the starting or moving-away idea more explicit.

So:

• Holnap korán indulunk. = neutral, natural
• Holnap korán elindulunk. = also natural, with a bit more emphasis on the act of setting off

In everyday speech, both can work depending on context.