Ona obično pristaje na dobar prijedlog, ali se ovaj put predomislila kad je čula koliko će put trajati.

The verb pristajati / pristati often goes with na + accusative when it means to agree to or to accept something.

So:

• pristati na prijedlog = to agree to / accept a proposal
• pristati na uvjete = to agree to the conditions

Here, na is not optional; it is part of how the verb is normally used in this meaning.

Because obično pristaje describes a habitual action: what she usually does in general.

• Ona obično pristaje... = She usually agrees...

Then the sentence contrasts that usual pattern with one specific past event:

• ali se ovaj put predomislila = but this time she changed her mind

So Croatian is doing the same thing English does in:

• She usually agrees, but this time she changed her mind.

Because prijedlog is a masculine inanimate noun, and after na here it is in the accusative.

For masculine inanimate nouns, the accusative singular looks the same as the nominative singular:

• nominative: dobar prijedlog
• accusative: dobar prijedlog

So even though the case has changed, the form stays the same.

A useful comparison:

• vidim dobar film = masculine inanimate, same form
• vidim dobrog čovjeka = masculine animate, different form

Here ovaj put means this time.

It is a very common expression:

• ovaj put = this time
• prvi put = first time
• zadnji put = last time
• svaki put = every time

So in this sentence it does not mean a physical road. It means on this occasion.

Because the verb is predomisliti se, which means to change one’s mind.

So:

• predomisliti se = to change one’s mind

The se is part of the verb as it is normally used. If you leave it out, you no longer have the standard everyday verb with that meaning.

This is a very common thing learners notice.

In the 3rd person singular perfect of reflexive verbs with se, Croatian normally has:

• ona se predomislila
• on se vratio
• ona se udala

not:

• ona se je predomislila
• on se je vratio

So se predomislila is the normal form here.

Compare other persons:

• ja sam se predomislila
• ti si se predomislila
• ona se predomislila
• mi smo se predomislili
• oni su se predomislili

Because the subject is ona, so the past participle agrees with a feminine singular subject.

Examples:

• on je čuo / predomislio se = masculine
• ona je čula / predomislila se = feminine
• ono je čulo = neuter

So the -la ending tells you the subject is feminine singular.

Because se is a clitic: a short unstressed word that normally appears near the beginning of the clause.

Croatian clitics such as se, je, će, sam, si usually go in second position in the clause.

So:

• ali se ovaj put predomislila

is natural because se comes very early, right after the clause opener ali.

This kind of word order is very typical in Croatian.

Both mean when.

• kad = shorter, very common in everyday speech and writing
• kada = a bit fuller, sometimes slightly more formal or emphatic

So:

• kad je čula
• kada je čula

both work here.

Because Croatian distinguishes between hearing and listening, just like English does.

• čuti = to hear
• slušati = to listen

In this sentence, the idea is that she heard how long the trip would last, and then changed her mind. So čula is the right choice.

Croatian often keeps the future tense in this kind of sentence if the action was still in the future at that moment.

So:

• kad je čula koliko će put trajati

literally corresponds to:

• when she heard how long the trip will last

But in natural English, we usually say:

• when she heard how long the trip would last

So this is one of those places where Croatian and English handle sequence of tenses differently. Croatian does not always backshift the tense the way English does.

Here koliko means how long / how much time.

That works because the verb trajati already means to last, so duration is clear from context.

• koliko će put trajati = how long the trip will last

You could also hear:

• koliko dugo će put trajati

That is a bit more explicit, but in this sentence koliko alone is perfectly natural.

Here put means trip / journey.

Croatian put can mean different things depending on context, including:

• road/path
• trip/journey
• time/occasion, as in ovaj put

So in this sentence:

• koliko će put trajati = how long the trip will last

Yes, putovanje could also be used:

• koliko će putovanje trajati

That sounds a little more explicit, but put is completely natural here.

Because Croatian has no articles.

So Croatian does not have direct equivalents of English a and the. Whether something is definite or indefinite is understood from context, word order, or other words such as ovaj.

So na dobar prijedlog could correspond to:

• to a good proposal
• to the good proposal

depending on context, though in natural English you would usually phrase that idea a bit differently.