Obično se budim u šest sati, ali danas sam se probudila kasnije.

Se is a reflexive particle, and with verbs like buditi se / probuditi se it means to wake up.

• buditi = to wake someone up
• buditi se = to wake up
• probuditi = to wake someone up completely / to awaken
• probuditi se = to wake up

So in this sentence, se is necessary because the speaker is the one waking up.

They come from two related verbs with different aspect:

• buditi se = imperfective
• probuditi se = perfective

In this sentence:

• Obično se budim uses the imperfective because it describes a habitual action: I usually wake up...
• sam se probudila uses the perfective because it describes one completed event today: I woke up...

This is a very common Serbian pattern:

• habitual / repeated action → imperfective
• one completed event → perfective

Because the sentence contrasts:

• a usual routine
• what happened today

So:

• Obično se budim... = I usually wake up... → present tense for habits
• danas sam se probudila... = today I woke up... → past tense for a specific event

Serbian often uses the present tense for things that usually happen, just like English does.

This is because sam and se are clitics, and Serbian clitics follow special word-order rules. They usually go near the beginning of the clause, in a fixed order.

In danas sam se probudila kasnije:

• sam = auxiliary am
• se = reflexive particle

The normal order is:

• sam se probudila

Not:

• se sam probudila

This clitic order is something learners gradually get used to, because it often does not match English word order.

Again, this is because of clitic placement. Se is a clitic, and it tends to appear in the second position of the clause.

So:

• Obično se budim = natural
• Obično budim se = unnatural

Here, Obično is the first element, so se comes right after it.

Because Serbian often drops subject pronouns when they are already clear from the verb form.

• budim already means I wake up
• sam se probudila also clearly means I woke up

So ja is not needed unless you want emphasis or contrast.

For example:

• Ja se obično budim u šest, a on u sedam. = I usually wake up at six, and he at seven.

Here ja is used for emphasis or contrast.

Because the past participle agrees with the gender of the speaker.

• probudila = feminine speaker
• probudio = masculine speaker

So this sentence was said by a woman or girl.

Compare:

• Danas sam se probudila kasnije. = said by a female
• Danas sam se probudio kasnije. = said by a male

This is one of the first things English speakers notice in Serbian past tense.

U šest sati means at six o’clock.

• u here means at
• šest = six
• sati = hours / o’clock in this expression

After numbers like 5 and above, Serbian commonly uses the genitive plural form:

• pet sati
• šest sati
• sedam sati

So u šest sati is the standard full expression for at six o’clock.

In everyday speech, people also often say simply:

• u šest

In this time expression, u is part of the phrase meaning at a certain hour.

The noun sati is in the form used after higher numbers, which is genitive plural.

So learners usually remember this as a fixed time expression:

• u jedan
• u dva
• u pet sati
• u šest sati

It is often easiest to learn the whole expression as a chunk rather than trying to analyze it too abstractly at first.

Kasnije means later.

It is the comparative form related to:

• kasno = late
• kasnije = later

So:

• Danas sam se probudila kasnije. = Today I woke up later.

The comparison is implied: later than usual.

Ali means but and introduces a contrast.

The contrast is:

• usually I wake up at six
• but today I woke up later

So ali connects the normal routine with the exception.

It is possible in some contexts, but it would not mean exactly the same thing.

• Obično se budim u šest sati focuses on a usual, repeated habit, using the imperfective verb.
• Obično se probudim u šest sati can sound more like I usually end up waking up at six or refer to the completed point of waking.

For beginners, the safest choice for habits like this is:

• obično + imperfective

So Obično se budim... is the most natural textbook example for a routine.

Some parts can move, but not freely.

For example, these are possible:

• Obično se budim u šest sati, ali danas sam se probudila kasnije.
• U šest sati se obično budim, ali danas sam se probudila kasnije.
• Danas sam se probudila kasnije.

But clitics like se and sam still have to follow Serbian clitic rules, so you cannot move them just anywhere.

Word order in Serbian is more flexible than in English, but it is not random. The movement usually changes emphasis, topic, or style.