Svo lengi sem strætóinn kemur á réttum tíma, verð ég stundvís í vinnunni.

It is a conjunction meaning as long as or so long as.

It introduces a condition:

• Svo lengi sem strætóinn kemur á réttum tíma = As long as the bus comes on time

This is a bit stronger and more ongoing than plain ef (if). It suggests that whenever this condition holds, the result will hold too.

Because -inn is the definite article attached to the noun.

• strætó = bus
• strætóinn = the bus

In Icelandic, the is usually not a separate word. It is added to the end of the noun instead.

Icelandic often uses the present tense for future meaning when the context makes it clear.

So:

• strætóinn kemur á réttum tíma literally looks like the bus comes on time
• but in natural English it can mean the bus arrives on time or if the bus comes on time

This is very normal in Icelandic, especially in conditions and everyday statements about what usually or expectedly happens.

Because á requires a certain case here, and in this expression it takes the dative.

So réttur tími changes to réttum tíma:

• réttur tími = nominative
• á réttum tíma = dative after á in this idiomatic time expression

Both the adjective and the noun change:

• réttur → réttum
• tími → tíma

The whole phrase á réttum tíma means on time or literally at the right time.

This is because Icelandic follows the V2 rule in main clauses: the finite verb usually comes in the second position.

Here, the sentence starts with the subordinate clause:

• Svo lengi sem strætóinn kemur á réttum tíma

After that, the main clause begins, and the finite verb comes first:

• verð ég stundvís í vinnunni

So the order is:

1. first element: the subordinate clause
2. second element: the verb verð
3. then the subject ég

If the sentence started directly with the main clause, you would say:

• Ég verð stundvís í vinnunni.

It is from verða, not vera.

• vera = to be
• verða = to become, and often to be / will be in a future-result sense

Here verð ég stundvís means something like:

• I become punctual
• more naturally: I will be punctual

So verða is often used when something results from a condition or change.

Because it describes the subject ég after the verb verða.

In other words:

• ég verð stundvís = I will be punctual

After vera and verða, Icelandic often uses an adjective as a subject complement:

• ég er þreytt(ur) = I am tired
• ég verð stundvís = I will be punctual

So stundvís is not an adverb here; it is describing the person.

It means at work or in/at the workplace.

• í = in
• vinnunni = the work / the workplace in the dative definite form

Because í is being used for location here, it takes the dative:

• vinnan = nominative definite
• í vinnunni = dative definite

In natural English, the whole phrase is often best understood as at work or for work, depending on context.

That ending shows both:

1. the definite article (the), and
2. the dative singular form

The base noun is:

• vinna = work

With the definite article in nominative singular:

• vinnan = the work

After í for location, it changes to dative:

• í vinnunni

So the ending is doing a lot of grammatical work at once.

Yes, but the nuance changes slightly.

• ef = if
• svo lengi sem = as long as / so long as

Compare:

• Ef strætóinn kemur á réttum tíma... = If the bus comes on time...
• Svo lengi sem strætóinn kemur á réttum tíma... = As long as the bus comes on time...

Ef is more neutral.
Svo lengi sem suggests an ongoing or repeated condition.

Because the sentence begins with a subordinate clause, and Icelandic normally separates that from the main clause with a comma.

So:

• Svo lengi sem strætóinn kemur á réttum tíma, verð ég stundvís í vinnunni.

That comma helps show the structure:

• subordinate clause first
• main clause second

This is very standard Icelandic punctuation.

Yes. In modern Icelandic, strætó is a very common everyday word for bus.

So:

• strætó = bus
• strætóinn = the bus

You may also notice that it behaves a little differently from some older noun patterns, but as a learner, the important thing is simply to recognize it as a common everyday noun.