Learn Finnish: Asiakas ihmettelee, miksi tämä kestää koko päivän. - The customer wonders why this takes the whole day.

In Finnish, you must always use a comma to separate an indirect question from the main sentence. Whenever you have a main clause like "The customer wonders..." followed by a question word like miksi (why), that comma is required!

Does the word order change because this is an indirect question?

No, and that makes it nice and easy! Whether it is a direct question (Miksi tämä kestää?) or an indirect one (...miksi tämä kestää.), the word order is exactly the same: question word + subject + verb.

I learned that kestää means 'to last'. Why is it translated as 'takes' here?

When talking about time, "lasting" and "taking" express the same idea. Tämä kestää koko päivän literally means "this lasts the whole day," which is just the normal way Finnish expresses that an action takes a certain amount of time.

Why does päivän have an -n ending?

When you want to say how long an action lasts (a duration), you put the time word in the genitive-looking accusative case. The -n ending on päivän shows that the action takes up one entire day from start to finish.

If päivän has an -n ending, why doesn't koko change to match it?