Conversation so far:
What was Warsaw like for E.T.A. Hoffman?
In Warsaw, E.T.A. Hoffmann found the same atmosphere he enjoyed in Berlin, renewing his friendship with Zacharias Werner, and meeting his future biographer, a neighbour jurist called Julius Eduard Itzig.
What was E. T. A. Hoffmann known for in Warsaw?
As chief Prussian administrator of the city from 1795 to 1806, E.T.A. Hoffmann was responsible for assigning surnames to Warsaw's Jewish community—a duty he executed based on whims.
Are there any interesting aspects about E. T. A. Hoffmann's time in Warsaw and assigning surnames to Jewish communities?
The names E.T.A. Hoffmann doled out would apparently depend on the day of the week.
What did E. T. A. Hoffmann say about the surnames to Jewish communities?
E.T.A. Hoffman said Monday the names of flowers, Friday the names of fish, or hung-over after drinking with Prussian army officer military names like Festung, Fojer, Pistolet, and Trompeter.
Anything else stood out about E. T. A. Hoffmann's time in Warsaw?
E.T.A. Hoffmann's fortunate position was not to last: on 28 November 1806, Napoleon Bonaparte's troops captured Warsaw, and the Prussian bureaucrats lost their jobs.
What happened when E. T. A. Hoffmann moved from Warsaw after Prussian bureaucrats lost their jobs?
E. T. A. Hoffmann arrived in Berlin on 18 June 1807, hoping to further his career there as an artist and writer.
Why did E. T. A. Hoffmann hope to further his career as artist and writer in Berlin?
Anything else interesting with E. T. A. Hoffmann after losing his job in Warsaw?
In January 1807, Hoffmann's wife and two-year-old daughter Cäcilia returned to Posen, while E. T. A. Hoffmann pondered whether to move to Vienna or go back to Berlin.
Who one did E. T. A. Hoffmann choose - his family or going back to Berlin?
As the French authorities refused to grant E.T.A. Hoffmann a passport to Vienna, he was forced to return to Berlin.

Question: When did he return
Self-contained rewrite: When did E. T. A. Hoffmann return to Berlin after being forced to go back?