La bienvenida terminó tarde.

Because bienvenida is functioning as a noun in this sentence, not as an adjective.

• la bienvenida = the welcome / the welcoming / the reception
• As a noun, it is feminine singular, so it takes la

Compare:

• Le dieron la bienvenida. = They welcomed him/her.
• Una calurosa bienvenida = a warm welcome

So in La bienvenida terminó tarde, la bienvenida is the subject of the sentence.

No. Bienvenida can be different things depending on context:

1. Noun
   • la bienvenida = the welcome
2. Adjective / past participle used adjectivally
   • Eres bienvenida aquí. = You are welcome here.
     (said to a woman)

Related forms:

• bienvenido = masculine singular
• bienvenida = feminine singular
• bienvenidos = masculine plural / mixed plural
• bienvenidas = feminine plural

In your sentence, it is definitely the noun.

Terminó is the preterite form of terminar and is used for a completed action in the past.

• La bienvenida terminó tarde. = the event ended late.

Why not the others?

• terminaba (imperfect) would suggest background, repetition, or an unfinished/ongoing past situation:
  • La bienvenida terminaba tarde cuando había discursos largos.
• ha terminado (present perfect) is also possible in some contexts, especially depending on region and how connected the event is to the present:
  • La bienvenida ha terminado tarde.

But for a simple finished past event, terminó is very natural.

The accent mark shows both pronunciation and meaning.

• terminó = he/she/it ended or ended (preterite, 3rd person singular)
• termino = I end (present tense)

So the accent helps distinguish:

• Yo termino = I finish / I end
• La bienvenida terminó = The welcome ended

It also tells you the stress falls on the last syllable: ter-mi-NÓ.

Because tarde here is an adverb, meaning late.

• terminó tarde = ended late

It is not the noun la tarde meaning the afternoon.

Compare:

• Terminó tarde. = It ended late.
• Terminó por la tarde. = It ended in the afternoon.

So in your sentence, tarde describes when the ending happened, not a specific noun.

Not in this sentence as written. Here, tarde naturally means late.

If you wanted to say in the afternoon, Spanish would usually say:

• por la tarde = in the afternoon

So:

• La bienvenida terminó tarde. = The welcome ended late.
• La bienvenida terminó por la tarde. = The welcome ended in the afternoon.

Those are different ideas.

Yes. Acabó is a very natural alternative to terminó.

• La bienvenida terminó tarde.
• La bienvenida acabó tarde.

Both mean basically the same thing: the welcome ended late.

A small note:

• terminar can sound a little more neutral/formal in some contexts.
• acabar is also extremely common and natural in everyday speech.

In most situations, either works well.

The subject is La bienvenida.

That is what terminated/ended.

Breakdown:

• La bienvenida = subject
• terminó = verb
• tarde = adverb

So the structure is:

[Subject] + [verb] + [adverb]

Yes, Spanish allows more flexibility than English.

You could also say:

• Terminó tarde la bienvenida.

That is grammatically possible, but La bienvenida terminó tarde is the most neutral and straightforward order.

Spanish often changes word order for:

• emphasis
• style
• rhythm
• context

For a learner, the original order is the safest default.

Because Spanish often does not need an explicit subject pronoun the way English does.

In English, you would say:

• It ended late.

In Spanish, the verb ending already helps identify the subject, and if the subject noun is present, no pronoun is needed:

• La bienvenida terminó tarde.

If the context were already clear, Spanish could even just say:

• Terminó tarde.

That would mean It ended late or She/he ended late, depending on context.

Yes. La bienvenida can refer to different kinds of welcome-related events or acts, depending on context.

It might mean:

• a welcome ceremony
• a welcoming event
• a reception
• a formal greeting
• a welcome speech, in some contexts

So the exact meaning depends on the situation, but grammatically the sentence stays the same.

They are related ideas, but they do not mean exactly the same thing.

• La bienvenida terminó tarde.
  = the event ended late
• La bienvenida duró hasta tarde.
  = the event lasted until late
• Se hizo tarde.
  = it got late

So:

• terminó tarde focuses on the end time
• duró hasta tarde focuses on the duration continuing late
• se hizo tarde focuses on time becoming late, not specifically the event ending

Yes, it is perfectly natural in Spain Spanish.

A speaker in Spain might also say things like:

• La bienvenida acabó tarde.
• El acto de bienvenida terminó tarde.
• La recepción terminó tarde.

But La bienvenida terminó tarde is grammatically correct and natural.