La riunione finisce alle diciannove, ma io preferisco uscire alle diciassette e trenta.

Because Italian normally uses a to mean at with clock times, and alle is the form you get from a + le.

So:

• alle diciannove = at 19:00
• alle diciassette e trenta = at 17:30

A useful extra point: for one o’clock, Italian uses all’una, not alle una.

Italian often uses the 24-hour clock, especially in formal contexts such as schedules, announcements, work, travel, and official writing.

So:

• diciannove = 19:00 = 7 p.m.
• diciassette e trenta = 17:30 = 5:30 p.m.

In everyday speech, Italians also very often use the 12-hour system, depending on context.

Yes, absolutely.

Both are correct:

• alle diciassette e trenta = more formal / 24-hour style
• alle cinque e mezza = more everyday conversational style

Likewise, alle diciannove could often be said as alle sette, if the context already makes it clear that you mean the evening.

That is true: Italian often drops subject pronouns because the verb ending already shows who the subject is.

So preferisco uscire already means I prefer to leave.

But io is added here for emphasis or contrast:

• ..., ma io preferisco... = ..., but I prefer...

It helps underline the contrast between what the meeting does and what I want to do.

Finisce is the third person singular present of finire.

The subject is la riunione = the meeting, which is singular, so the verb must also be singular:

• la riunione finisce = the meeting ends

This is just the normal present-tense form for he/she/it ends.

Because preferire belongs to a group of -ire verbs that add -isc- in some present-tense forms.

So the present tense is:

• io preferisco
• tu preferisci
• lui/lei preferisce
• noi preferiamo
• voi preferite
• loro preferiscono

So preferisco is the correct I prefer form.

Because after preferire, Italian usually uses another verb in the infinitive.

So:

• preferisco uscire = I prefer to leave / I prefer leaving

This is very common in Italian:

• voglio andare = I want to go
• devo studiare = I have to study
• posso entrare = I can come in

The first verb is conjugated; the second stays in the infinitive.

It can mean both, depending on context.

The core idea is to go out / exit. In this sentence, because we are talking about a meeting, uscire is naturally understood as:

• to leave
• more literally, to go out

So preferisco uscire alle diciassette e trenta means I’d rather leave at 5:30.

Because riunione is a feminine singular noun, so it takes the feminine singular definite article la.

• la riunione = the meeting

This is something you generally have to learn with the noun itself. The ending -ione often appears in feminine nouns, and riunione is one of them.

Italian often uses the present tense for scheduled events or plans, just as English can.

So:

• La riunione finisce alle diciannove literally uses the present, but it can refer to a scheduled ending time.

This feels natural in Italian when talking about timetables, routines, or arranged events.

You could sometimes use a future form in other contexts, but the present here is completely normal.

It literally means and thirty.

Italian commonly tells time this way:

• diciassette e trenta = 17 and 30
• otto e dieci = 8:10
• nove e venti = 9:20

So e really is just and when giving the minutes after the hour.

A rough English-friendly guide:

• riunione ≈ ryoo-NYO-neh
• finisce ≈ fee-NEE-sheh
• preferisco ≈ preh-feh-REE-sko
• uscire ≈ oo-SHEE-reh
• diciassette ≈ dee-cha-SAHT-teh
• diciannove ≈ dee-chan-NOH-veh

Two useful pronunciation notes:

• sci in uscire sounds like shee
• ce / ci often sound like che / chi in English, so finisce ends with a sheh sound, not a hard skeh sound