Translation:They have three weeks to sell that building.
(native speaker here)
In another question I answered to a similar question or maybe it was this same other way around. I can't say for sure, but I reason this way. What have they? They have time, aikaa. How much of it have they? Kolme viikkoa. So three weeks is an attribute to the time.
I asked my family members whether they would accept the sentence without. The votes scored draw, but after a while one without-supporter changed her mind and noticed, that you almost automatically put aikaa. So while perhaps grammatically somehow possible, it sounds strange.
Does it matter when aikaa (time) appears, or not, in the example sentence? In a previous example, using "... we have two weeks to buy", the word "time" is not in the sentence to be translated, but the answer was wrong if it did not include "aikaa" (kaksi viikkoa aikaa). This makes me wonder if an inference tells when to include "aikaa" in the answer, and when to exclude "aikaa" from the answer even though "aikaa" is included in the sentence to be translated, such as seen here.
I am not sure what you are asking, but…
As you can see from the discussion here, the Finnish sentence requires aikaa, it is the object of having. In English you seem to be able to leave it out or if used, the time expression must be in genitive, e.g. three weeks’ time.