Conversation so far:
What did Yip Harburg do in his early life?
Yip Harburg attended Townsend Harris High School, where he and Ira Gershwin worked on the school paper and became lifelong friends.
Did Yip Harburg go to college?
After World War I, Yip Harburg returned to New York and graduated from City College - later part of the City University of New York, in 1921.
What did Yip Harburg do after college?
After Yip Harburg married and had two children, he started writing light verse for local newspapers.
What else did Yip Harburg do besides writing for the local newspapers?
Yip Harburg became a co-owner of Consolidated Electrical Appliance Company, but the company went bankrupt following the crash of 1929.
What did Yip Harburg do at Consolidated Electrical Appliance Company?
Yip Harburg was co-owner of Consolidated Electrical Appliance Company.

Question: How long was he co owner?
Self-contained rewrite: How long was Yip Harburg co-owner of Consolidated Electrical Appliance Company?