Learn Hardcore Croatian: Sinoć smo dugo gledali seriju. - Last night we watched a series for a long time.

sinoć = specifically the last night (one word, very common)
jučer navečer = yesterday evening, focuses more on the evening part of yesterday

They often overlap in practice, but:

If you say sinoć, people imagine sometime during the previous night (could be late).
If you say jučer navečer, it sounds more like the earlier part of the evening of yesterday.

In your sentence, Sinoć smo dugo gledali seriju, English Last night we watched a series for a long time is the best match.

Why is smo in the second position, right after sinoć?

Smo is a clitic form of the auxiliary verb biti (to be) used to form the past tense. In Croatian, clitics have to stand in the so‑called second position in the sentence: they normally come right after the first stressed word or phrase.

In Sinoć smo dugo gledali seriju:

first stressed word: Sinoć
second position: smo

So the order has to be:

✅ Sinoć smo dugo gledali seriju.

but not:

❌ Sinoć dugo smo gledali seriju. (here smo is not in second position)

If you start the sentence differently, the clitic moves accordingly:

Dugo smo sinoć gledali seriju. (first word Dugo, clitic smo second)
Mi smo sinoć dugo gledali seriju. (first word Mi, clitic smo second)
Gledali smo sinoć dugo seriju. (first word Gledali, clitic smo second)

What is smo gledali grammatically, and how is the past tense formed here?

The Croatian past tense (perfect) is formed with:

present tense of biti (to be) + past participle of the main verb

In your sentence:

auxiliary (present of biti): smo (1st person plural = we are)
past participle of gledati: gledali

So smo gledali literally means we have watched / we were watching, but in Croatian it’s just the normal way to say we watched / we were watching.

Full paradigm of gledati in the past (masc. subject unless noted):

Ja sam gledao / gledala – I watched
Ti si gledao / gledala – You watched (sg.)
On je gledao – He watched
Ona je gledala – She watched
Ono je gledalo – It watched
Mi smo gledali / gledale – We watched
Vi ste gledali / gledale – You watched (pl.)
Oni su gledali – They watched (m. or mixed)
One su gledale – They watched (fem.)
Ona su gledala – They watched (neut. plural, rarely used with people)

So Sinoć smo dugo gledali seriju = Last night we watched (for a long time) a series.

Why is it gledali and not gledale or gledao in this sentence?

The past participle in Croatian agrees with the subject in gender and number.

gledao – masculine singular (one male, or grammatically masculine noun)
gledala – feminine singular (one female, or grammatically feminine noun)
gledali – masculine plural or mixed group (at least one male)
gledale – feminine plural (all female group)

In Sinoć smo dugo gledali seriju, the default assumption is that mi (we) is either:

a group of men, or
a mixed group (men + women)

If the group was exclusively female, you would say:

Sinoć smo dugo gledale seriju.

Can the word order change? For example, can I say Dugo smo sinoć gledali seriju or Gledali smo dugo seriju sinoć?

Yes, Croatian word order is quite flexible, as long as clitics like smo stay in the second position. All of these are grammatically correct, but they differ slightly in emphasis:

Sinoć smo dugo gledali seriju.
Neutral; you first anchor the time (sinoć), then mention that it was for a long time.
Dugo smo sinoć gledali seriju.
Emphasises how long you watched (the dugo is more prominent).
Sinoć smo seriju dugo gledali.
Slightly marked; focuses more on watching that series for a long time.
Gledali smo sinoć dugo seriju.
Also possible; sounds a bit more informal, with light emphasis on the activity gledali.

What you cannot do is break the clitic rule, e.g.:

❌ Sinoć dugo smo gledali seriju. (clitic not in second position)

What does dugo mean here? Does it mean “for a long time,” and can I put it somewhere else in the sentence?

Dugo is an adverb meaning for a long time / long in a temporal sense.

In Sinoć smo dugo gledali seriju, it means we watched for a long time.

You can move dugo, as long as the clitic rule is respected. Common variants:

Sinoć smo dugo gledali seriju.
Dugo smo sinoć gledali seriju.
Sinoć smo gledali seriju dugo. (a bit less common, often used for emphasis)
Gledali smo dugo sinoć seriju. (informal, but okay)

All keep the meaning of a prolonged action. For a specific duration you’d say, for example:

Sinoć smo tri sata gledali seriju. – We watched the series for three hours last night.

Why is it seriju and not serija?

Seriju is the accusative singular form of the noun serija (series, TV show).

Serija is a feminine noun. Its basic forms (singular) are:

Nominative: serija – subject (This series is good)
Genitive: serije – of the series
Dative: seriji – to/for the series
Accusative: seriju – direct object (we watched the series)
Vocative: serijo – used when addressing (rare for this word)
Locative: (o) seriji – about/in the series
Instrumental: serijom – with/by the series

In Sinoć smo dugo gledali seriju, seriju is the direct object of gledali, so it must be in the accusative case.

In English I’d say either “a series” or “the series.” How do you know which one seriju means if there are no articles?

Croatian has no articles like a or the, so seriju on its own can mean either a series or the series, depending on context.

If the series has already been mentioned or is understood from context, seriju = the series:
- Sinoć smo dugo gledali seriju koju si mi preporučio.
  – Last night we watched the series you recommended to me (a specific one).
If it’s just some series, with no specific one in mind, seriju ~ a series.

If you want to make the indefiniteness explicit, you can use jednu (one):

Sinoć smo dugo gledali jednu seriju. – Last night we watched a (some) series for a long time.

But very often, seriju alone is enough and the context clarifies whether it’s a or the.

Does serija in Croatian always mean a TV series, or can it mean other things?

In everyday language, serija almost always means a TV show / TV series, including streaming series. In this sentence, that is the natural interpretation.

However, serija can also mean series more generally, for example:

serija članaka – a series of articles
serija brojeva – a series of numbers

In the context of watching (gledati seriju), people strongly assume TV series. You don’t need to say TV seriju unless you really want to stress that it’s on TV.

What is the difference between gledati and pogledati / odgledati in a sentence like this?

This is about aspect (imperfective vs. perfective):

gledati – imperfective: focuses on the process, duration, or habit
- Sinoć smo dugo gledali seriju.
  – We spent a long time watching the series (emphasis on duration).
pogledati or odgledati – perfective: focuses on the completion of the action
- Sinoć smo pogledali seriju.
  – We finished the series last night (watched it to the end).
- Sinoć smo odgledali cijelu seriju.
  – We watched the whole series (often implies all episodes, or a whole season, depending on context).

So your original sentence emphasises that you were watching for a long time, without saying whether you finished the whole series.

In English I can say “we watched a series” or “we were watching a series.” Does Sinoć smo dugo gledali seriju cover both meanings?

Yes. Croatian does not have a separate past continuous form like English were watching.

Sinoć smo dugo gledali seriju can correspond to:

Last night we watched a series for a long time.
Last night we were watching a series for a long time.

If you need to show that something else happened during that watching, you just add the second event with another past tense:

Sinoć smo dugo gledali seriju kad je nestalo struje.
– Last night we were watching a series for a long time when the power went out.

The combination of imperfective verb (gledati) and context tells you that it was an ongoing action.

Can sinoć move to another place in the sentence, or must it stay at the beginning?

Sinoć is an adverb of time, and it can move quite freely. Common positions include:

Sinoć smo dugo gledali seriju.
Dugo smo sinoć gledali seriju.
Gledali smo sinoć dugo seriju.
Gledali smo dugo sinoć seriju. (a bit less usual, but possible)

As long as:

The clitic smo remains in second position relative to the first stressed word/phrase.
The sentence remains clear.

Positioning sinoć at the beginning is very natural because it sets the time frame right away.