Yesterday I was discussing the subject of caring for elderly parents in a private message with another LERNU user. At first, I wrote the following sentence:

Esperanto: La gepatrojn mi ankaŭ vartis dum 11 jaroj, dum kiuj mi nur portempe laboris profesie.

English intent: I also took care of my parents for 11 years, during which I only worked professionally on a part-time basis.

(I assume the Esperanto above is correct. Please let me know if it is not)

Next, I did some self-editing, and changed "dum 11 jaroj" to "11 jarojn". Still correct, ĉu ne?

Finally, I decided to change "dum kiuj" (referring to the "years") to just "kiujn", because I had used the accusative of time in the previous clause, and the reference was still to time in the subordinate clause. My final version of the Esperanto sentence turned out as follows:

La gepatrojn mi ankaŭ vartis 11 jarojn, kiujn mi nur portempe laboris profesie.

So, the question is: can or should one use the accusative of time with "kiuj" if it's antecedent is also an accusative of time?

You would have to say "dum kiuj" here. "Kiujn" wouldn't work.

The difference is that "11 jaroj" is obviously a period of time, so when you say "11 jarojn", it's clear that we're talking about a time period. "kiujn" is *not* clearly talking about a time period.

If you were to say "kiujn" in your example sentence, personally, I would assume you were referring to the parents (the most obvious plural noun in the first half of the sentence), and it would be confusing to hear what followed that word "kiujn".

As for the original sentence, "dum 11 jaroj" and "11 jarojn" are both correct. But since you already have a direct object (la gepatrojn), I personally prefer the form "dum 11 jaroj". We want to speak with the maximum clarity, and two -n endings, where one is for direct object and one is for duration of time, is somewhat less clear than using -n for a direct object and a preposition for showing time. It's correct both ways but in my opinion it does add a bit of additional clarity if you avoid repeating grammatical forms.

erinja: "kiujn" is *not* clearly talking about a time period.

Thanks for your time and comments, as usual. That is exactly what I was looking for!