He llegado is the present perfect: I have arrived. In Spain, this tense is very commonly used for actions connected to the present moment.
Here, the speaker is apologizing for something that has just happened or is still relevant now: they are late right now.
Compare:
In many parts of Spain, he llegado tarde sounds very natural in this kind of immediate situation.
Yes, literally it does. But in natural English, you would often translate it simply as:
So even though the Spanish structure is I have arrived late, the best English translation depends on the situation.
Spanish often leaves out subject pronouns because the verb form already shows who is doing the action.
So yo is not necessary. You could say Yo he llegado tarde, but it would usually sound unnecessary unless you want emphasis, contrast, or clarification.
Here, tarde is an adverb, meaning late.
It describes how the person arrived:
Because it is an adverb here, it does not change for gender or number.
Compare:
In the sentence you gave, tarde is the fixed form you want.
Yes. Llegar tarde is the normal way to say to arrive late.
Examples:
It is a very common and useful expression.
Yes, depending on the tone.
Common options are:
All are possible, but Disculpe is especially appropriate if you want to sound respectful.
You would normally change Disculpe to Disculpa if speaking to one person informally.
So:
If you are talking to friends or people your age in a casual setting, this is more natural.
Yes, it is completely natural and can stand on its own.
Disculpe, he llegado tarde. is a clear, polite apology.
If you want to sound a bit fuller or more apologetic, you could add something like:
They are related, but not the same.
If you are already there and apologizing for being late, he llegado tarde works very well.
If you are on the way or speaking more generally about the situation, llego tarde may fit better.