Lunde mi havas rendevuon kun mia kuracisto, sed marde mi laboras la tutan tagon.

In Esperanto, names of days are nouns:

• lundo = Monday
• mardo = Tuesday

When you change them to -e forms, they work like adverbs of time:

• lunde = on Monday / Monday
• marde = on Tuesday / Tuesday

So:

• Lunde mi havas rendevuon... = On Monday I have an appointment...
• ...sed marde mi laboras... = ...but on Tuesday I work...

This is a very common and natural way to talk about days in Esperanto.

Usually, no. The normal way is simply:

• lunde
• marde

Esperanto often expresses time very directly, without a preposition. Using the adverb form of the weekday is the standard choice here.

Because rendevuon is the direct object of havas.

• havi = to have
• what do I have? rendevuon

In Esperanto, direct objects take -n:

• Mi havas libron. = I have a book.
• Mi havas rendevuon. = I have an appointment.

So the -n here marks rendevuon as the thing being had.

Here, rendevuo means appointment.

So mi havas rendevuon kun mia kuracisto means:

• I have an appointment with my doctor

In some contexts, rendevuo can also mean a planned meeting, and sometimes even a romantic date, depending on context. But with kuracisto, it clearly means a medical appointment.

Because kun is a preposition, and after a normal preposition you generally do not use the accusative -n.

• kun mia kuracisto = with my doctor

Here:

• mia describes kuracisto
• kuracisto is not the direct object of the verb
• it is part of a prepositional phrase introduced by kun

So the correct form is:

• kun mia kuracisto

not:

• kun mian kuraciston

Kuracisto means doctor.

It can be understood as:

• kuraci = to treat medically
• -ist- = a person who does a profession or activity
• -o = noun ending

So kuracisto is literally something like a person who treats medically.

Esperanto often does not need a separate preposition like English on for days and dates.

English says:

• on Monday
• on Tuesday

Esperanto usually just says:

• lunde
• marde

So the idea of on is already built into the time expression.

Yes. Sed means but.

It connects two contrasting ideas:

• Lunde mi havas rendevuon kun mia kuracisto
• sed
• marde mi laboras la tutan tagon

So the speaker is contrasting Monday and Tuesday.

Mi laboras is the normal, simple way to say I work / I am working.

Esperanto often uses the simple present tense where English might use either:

• I work
• I am working

So here:

• mi laboras la tutan tagon = I work all day / I am working the whole day

The longer form mi estas laboranta exists, but it is usually used only when you specifically want to emphasize the ongoing nature of the action.

This is a very common Esperanto pattern: the accusative -n can show duration of time.

So:

• la tutan tagon = the whole day / all day

Literally, it is a time expression marked with -n.

You will often see similar examples:

• Mi dormis la tutan nokton. = I slept the whole night.
• Ŝi laboris du horojn. = She worked for two hours.

So in this sentence, tagon is not the direct object of laboras. The -n is showing how long the action lasts.

Both can make sense in Esperanto, but la tutan tagon is very natural when you mean the whole day as a complete, definite span.

• la tutan tagon = the whole day / all day

Here:

• tuta = whole, entire
• la helps make it a specific complete unit: the entire day

This is the most common way to say all day in a sentence like this.

Because tutan is an adjective modifying tagon, and adjectives in Esperanto agree with the nouns they describe.

• taga would not be correct here
• the base adjective is tuta = whole

Since tagon is:

• singular
• accusative (-n)

the adjective must match it:

• tutan tagon

Compare:

• la tuta tago = the whole day
• la tutan tagon = the whole day (as a duration expression)

Not completely. Esperanto word order is fairly flexible because endings show grammatical roles.

The original sentence is perfectly natural:

• Lunde mi havas rendevuon kun mia kuracisto, sed marde mi laboras la tutan tagon.

But other orders are also possible, for example:

• Mi havas rendevuon kun mia kuracisto lunde...
• Marde mi laboras la tutan tagon.

Putting Lunde and marde at the beginning gives them emphasis and makes the contrast between the two days especially clear.

In Esperanto, stress is almost always on the second-to-last syllable.

So:

• LUN-de
• mi
• HA-vas
• ren-de-VU-on
• kun
• MI-a
• ku-ra-CIS-to
• sed
• MAR-de
• mi
• la-BO-ras
• la
• TU-tan
• TA-gon

That regular stress pattern is one of the things that makes Esperanto pronunciation predictable.