Li poste konfesis, ke mi ne eraris pri la horo de la kunveno.

It has two parts:

• Li poste konfesis = the main clause
• ke mi ne eraris pri la horo de la kunveno = a subordinate clause introduced by ke

So the pattern is:

[main statement] + ke + [what was admitted/confessed]

This works a lot like English that-clauses.

Poste means later, afterward, or later on.

So Li poste konfesis means that the confession/admission happened after some earlier event or discussion.

Esperanto word order is fairly flexible, so you could also see:

• Li konfesis poste...

But Li poste konfesis... is very natural.

It comes from konfesi, which can mean to confess, but in many everyday contexts it is closer to to admit.

So here it does not have to sound dramatic or religious. It can simply mean:

• he later admitted
• he later acknowledged

That is often the most natural English sense.

Ke means that and introduces a subordinate clause.

So:

• Li poste konfesis, ke... = He later admitted that...

The comma before ke is very common in Esperanto when introducing this kind of clause. Esperanto punctuation is somewhat flexible, but many writers use the comma here because it clearly separates the main clause from the subordinate clause.

Eraris is the past tense of erari.

It is past because the sentence is talking about a past situation: at that earlier time, the speaker was not mistaken about the meeting time.

A useful point: in Esperanto, you normally choose the tense based on the meaning you want, not because of an automatic English-style tense shift. So:

• ne eraris = was not mistaken
• ne eraras = am not mistaken

Here ne eraris fits the past situation.

Erari means to make a mistake, to be wrong, or to be mistaken.

So mi ne eraris means:

• I was not mistaken
• I wasn’t wrong

This is a very normal Esperanto way to express the idea.

You could also say:

• Li poste konfesis, ke mi pravis pri la horo de la kunveno.

That would mean He later admitted that I was right about the meeting time.

The difference is mostly one of emphasis:

• mi ne eraris = I was not mistaken
• mi pravis = I was right

These are close in meaning, but not always identical in tone. Ne eraris focuses on the absence of error; pravis focuses more directly on correctness.

Because erari pri io is a standard Esperanto pattern meaning to be mistaken about something.

So:

• erari pri la horo = to be mistaken about the time
• erari pri la adreso = to be mistaken about the address

The preposition pri often means about or concerning, and that is exactly the idea here.

Horo usually refers to a specific hour or clock time.

Tempo is broader and means time in a more general sense.

So if the issue is the scheduled time of the meeting, la horo de la kunveno is the natural choice.

Compare:

• la horo de la kunveno = the meeting’s time / the hour of the meeting
• la tempo de la kunveno = the time period of the meeting, or a more general notion of its timing

De la kunveno means of the meeting.

So la horo de la kunveno is literally the hour/time of the meeting, meaning the meeting’s scheduled time.

It does not mean at the meeting.

If you wanted at the meeting, you would use something like:

• ĉe la kunveno = at the meeting
• dum la kunveno = during the meeting

Because both things are understood as specific:

• la kunveno = the specific meeting being discussed
• la horo = the specific time of that meeting

Esperanto uses la when the noun is definite, much like English the.

Because horo comes after the preposition pri:

• pri la horo

After a preposition, nouns normally do not take -n.

So:

• pri la horo = about the time
• not pri la horon

Likewise, de la kunveno also has no -n, because de is a preposition too.