Ĵaŭdo estos longa tago por ni, ĉar ni havos kunvenon je la oka.

Not usually. In Esperanto, days of the week are normally written in lowercase, just like ordinary nouns: lundo, mardo, merkredo, ĵaŭdo, and so on.

Here it is capitalized simply because it is the first word of the sentence.

So:

• ĵaŭdo = Thursday
• Ĵaŭdo = Thursday at the beginning of a sentence

Estos is the future tense of esti = to be.

Esperanto verb endings are very regular:

• estas = is / am / are
• estis = was / were
• estos = will be
• estus = would be
• esti = to be

So Ĵaŭdo estos longa tago means Thursday will be a long day.

Because longa tago is the predicate after the verb esti.

After esti, Esperanto does not use the accusative -n for the complement. So:

• Tio estas bona ideo. = That is a good idea.
• La tago estos longa. = The day will be long.

In your sentence, longa tago describes what Thursday will be, so no -n is needed.

Because the sentence is not saying Thursday will be the long day. It is saying Thursday will be a long day in a general descriptive sense.

Esperanto uses la only for something definite and specifically identified. Here, longa tago is just a description.

Compare:

• Ĵaŭdo estos longa tago. = Thursday will be a long day.
• Ĵaŭdo estos la plej longa tago. = Thursday will be the longest day.

Por ni means for us.

• por = for
• ni = we / us

In this sentence, it shows who experiences the day as long:

• longa tago por ni = a long day for us

It does not mean possession. It is more about perspective or effect.

Yes. Ĉar is the standard Esperanto conjunction for because.

It introduces a reason:

• Ni restis hejme, ĉar pluvis. = We stayed home because it was raining.
• Ĵaŭdo estos longa tago por ni, ĉar ni havos kunvenon... = Thursday will be a long day for us, because we will have a meeting...

It connects two clauses, just like English because.

Because kunvenon is the direct object of havos.

• havi = to have
• kunveno = meeting
• kunvenon = meeting, as a direct object

Esperanto marks direct objects with -n. So:

• Ni havos kunvenon. = We will have a meeting.

That -n shows what is being had.

Kunveno usually means meeting, gathering, or assembly, depending on context.

It comes from:

• kun- = together
• veni = to come

So the basic idea is a coming together.

In many everyday contexts, kunveno is the normal word for a meeting:

• a work meeting
• a committee meeting
• a group gathering

So here ni havos kunvenon naturally means we will have a meeting.

Because Esperanto often expresses clock time with an understood ordinal hour.

• oka = eighth
• je la oka literally means at the eighth [hour]
• in natural English, that becomes at eight o’clock

The noun horo is understood, so je la oka is a shortened form of je la oka horo.

This is a very common way to tell time in Esperanto.

Because the expression refers to the eighth hour, not just the number eight by itself.

• ok = eight
• oka = eighth

So:

• je la oka = at eight o’clock
• literally: at the eighth [hour]

This is different from counting objects:

• ok libroj = eight books
• la oka libro = the eighth book

Time expressions often use the ordinal form in Esperanto.

Je is a very general preposition in Esperanto, often used when no more specific preposition is standard or when talking about clock times.

For time of day, je is very common:

• je la tria = at three o’clock
• je la sepa = at seven o’clock
• je la oka = at eight o’clock

So in your sentence, je marks the time when the meeting will happen.

Yes. Je la oka horo is correct and a little more explicit.

Both mean the same thing:

• je la oka = at eight o’clock
• je la oka horo = at the eighth hour / at eight o’clock

Usually, speakers leave out horo because it is understood.

A native English speaker often notices the special letters right away.

• ĵ sounds like the s in measure or the g in mirage
• ĉ sounds like ch in church
• ŭ is a short glide, like the w part in cow or now

So:

• Ĵaŭdo sounds roughly like ZHOU-do
  
  • ĵaŭ rhymes approximately with now, but begins with the zh sound
• ĉar sounds roughly like char

The pronunciation is very regular in Esperanto: each letter has one main sound.

Esperanto word order is fairly flexible, though some orders sound more natural than others.

The given sentence is very natural:

• Ĵaŭdo estos longa tago por ni, ĉar ni havos kunvenon je la oka.

You could move some parts for emphasis, for example:

• Ĉar ni havos kunvenon je la oka, ĵaŭdo estos longa tago por ni.
• Je la oka ni havos kunvenon.

But the original order is straightforward and probably the most neutral for a learner to use.

Because ĉar introduces a subordinate clause giving the reason, and it is normal in Esperanto to separate such clauses with a comma.

So the structure is:

• main clause: Ĵaŭdo estos longa tago por ni
• reason clause: ĉar ni havos kunvenon je la oka

The comma helps show that division clearly.