Post breve spatium otii discipuli iterum libros legunt.

Post is a preposition meaning after. When post is used as a preposition in Latin, it takes the accusative case.

So in this sentence:

• post = after
• breve spatium = a short period / a short space of time

That is why spatium is in the accusative: post breve spatium.

Because breve has to agree with spatium.

• spatium is neuter singular
• so the adjective must also be neuter singular
• the accusative singular neuter of brevis is breve

So:

• brevis = nominative singular masculine/feminine
• breve = nominative or accusative singular neuter

Since spatium is neuter and is here in the accusative, breve is the correct form.

Otii is genitive singular of otium, meaning leisure, rest, or free time.

It depends on spatium and helps describe what kind of period it is:

• spatium otii = a period of leisure / a period of rest

So otii is not the object of anything. It is a genitive modifying spatium.

Latin word order is much more flexible than English word order. The sentence begins with the time expression:

• Post breve spatium otii = After a short period of rest

This sets the scene first. Then we get the subject:

• discipuli = the students

This is very natural in Latin. English often prefers The students read again after a short break, but Latin can easily begin with the time phrase instead.

We know from both case and verb ending.

• discipuli is nominative plural
• legunt means they read

Those match perfectly:

• discipuli = the students
• legunt = they read

So discipuli is the subject of the sentence.

Because libros is the direct object of legunt.

• lego, legere = to read
• what do they read? books
• therefore books must be in the accusative

So:

• libri = books as a subject
• libros = books as an object

Here the students are doing the action of reading to libros, so accusative is required.

Iterum is an adverb meaning again.

It tells us that the action happens another time:

• discipuli iterum libros legunt = the students read books again

Its position is flexible. Latin adverbs can often move around without changing the basic meaning very much. Here it sits before libros legunt, which is a very normal placement.

Putting the verb at the end is very common in Latin, though it is not required.

So this pattern is very typical:

• time phrase
• subject
• object
• verb

Here we get:

• Post breve spatium otii = time phrase
• discipuli = subject
• iterum libros = adverb + object
• legunt = verb

Latin often saves the verb for the end, but other word orders are possible too.

It can mean either, depending on context.

The Latin present tense often covers both:

• they read
• they are reading

So legunt could be understood as either they read or they are reading. English has to choose more explicitly, but Latin usually does not.

Because Latin has no articles.

There is no separate word for:

• the
• a / an

So discipuli can mean:

• students
• the students

And libros can mean:

• books
• the books

The context and the translation decide which English article sounds best.

Literally, spatium can mean space, distance, interval, or period of time. In this sentence, because of post and otii, it clearly refers to a period of time:

• breve spatium otii = a short period of leisure/rest

So although spatium can have a spatial meaning, here it is temporal.