I want to know the answer to the following question:
How long was the city completely empty?
All the background I'm provided with is that "Between the German invasion of Poland on 1 September 1939 and the Anglo-French declaration of War against the German Reich on 3 September 1939, the entire city (a total of 120,000 people) was evacuated, like other border towns as well.". Is that enough to answer the question?
Answer: no