U rujnu i listopadu vraćamo se redovitom rasporedu i opet više učimo nego ljeti.

Because after u meaning in for time expressions, Croatian normally uses the locative case.

• rujan → u rujnu
• listopad → u listopadu

So:

• u rujnu = in September
• u listopadu = in October

This is very common with months:

• u siječnju = in January
• u travnju = in April
• u prosincu = in December

If u meant movement into something, it would often take the accusative, but here it means during / in a month, so locative is used.

Because one preposition can govern both nouns when they are joined by i = and.

So u rujnu i listopadu literally means:

• in September and October

Croatian does not need to repeat the preposition:

• u rujnu i listopadu
  not necessarily
• u rujnu i u listopadu

Both are possible in some contexts, but using u once is the normal, natural way here.

Vraćati se / vratiti se means to return, to come back.

The se is a reflexive particle that belongs to the verb. In many cases, you should learn this as part of the verb itself:

• vraćati = to return something, to bring back
• vraćati se = to return, to come back

Examples:

• Vraćam knjigu. = I am returning the book.
• Vraćam se kući. = I am returning home.

So in your sentence:

• vraćamo se = we return / we are returning / we go back

It is not optional here.

The verb vraćati se commonly takes the dative when it means return to something.

That is why you get:

• redovitom rasporedu = to the regular schedule

This is the dative singular form of:

• redoviti raspored = regular schedule

So the structure is:

• vraćati se + dative
• vraćamo se redovitom rasporedu = we are returning to the regular schedule

You may also see other Croatian verbs that require dative where English uses to.

It is dative singular.

Base form:

• redoviti raspored = regular schedule

In the dative singular:

• redoviti → redovitom
• raspored → rasporedu

So:

• redovitom rasporedu = to the regular schedule

This is a very typical masculine adjective + noun pattern in the dative singular.

Croatian clitics such as se usually go in the second position in the clause.

So:

• U rujnu i listopadu vraćamo se redovitom rasporedu...

is natural because se follows the first stressed element of its clause, here the verb phrase arrangement after the initial time expression.

You may also hear different word orders in Croatian, because word order is flexible, but clitics still follow special placement rules. For learners, it is often best to remember that se usually cannot just go anywhere.

Because Croatian often uses the present tense for:

• habitual actions
• scheduled actions
• general statements about a period of time
• sometimes near-future meaning

Here it means something like:

• In September and October, we go back to the regular schedule...

It sounds natural in Croatian to describe what happens during that period using the present tense.

Opet means again.

So:

• i opet više učimo = and we again study more / and we study more again

In natural English, you would usually say:

• and we study more again
• or more idiomatically, and we start studying more again

Croatian word order is flexible, and opet is placed before what it modifies naturally in the sentence.

Here više means more.

So:

• više učimo = we study more / we learn more

This is više as a comparative adverb, not više meaning no longer.

Compare:

• Učimo više nego prije. = We study more than before.
• Ne učim više. = I no longer study.

In your sentence, the presence of nego ljeti makes it clear that this is the comparative more.

This is the standard Croatian comparative structure:

• više ... nego ... = more ... than ...

So:

• više učimo nego ljeti = we study more than in summer

Other examples:

• Radi više nego prije. = He/She works more than before.
• Ona čita više nego ja. = She reads more than I do.

This is very similar to English more ... than ....

Because ljeti is an adverb meaning in summer / during the summer.

It is a common time expression, similar to:

• zimi = in winter
• ljeti = in summer

So:

• nego ljeti = than in summer

This is more natural than u ljetu, which is generally not how Croatian expresses this idea.

Grammatically, učiti can be connected to both ideas, but in this sentence we study is usually the more natural English translation.

• učiti can mean to study
• it can also mean to learn, depending on context

Here, because of returning to the regular schedule, the idea is probably:

• we study more than in summer

That sounds more natural in English than we learn more than in summer, although the Croatian itself allows the broader idea of learning/studying.

Because the two i's do different jobs.

1. u rujnu i listopadu
   Here i joins two nouns:

   • September and October

2. ... redovitom rasporedu i opet više učimo ...
   Here i joins two actions or statements:

   • we return to the regular schedule and again study more

So both are just the normal conjunction and, used in two different places.

Yes, regularnom rasporedu is possible, but redovit raspored is a very natural and common Croatian phrase.

Both adjectives can be translated as regular in English, but their usage can vary by context and collocation. In this sentence, redovitom rasporedu sounds perfectly natural and idiomatic.

It sounds more like a general or habitual situation.

The sentence suggests that in September and October:

• we go back to the regular schedule
• we study more than in summer

That feels like a seasonal routine, not one single moment. The use of the present tense supports that interpretation.