Conversation so far:
What was something Robert Hughe the critic did in his personal life?
Robert Hughes met his first wife, Danne Emerson, in London in 1967. Together they became involved in the counterculture of the 1960s, exploring drug use and sexual freedom.
When did Robert Hughes the critic get married?
Robert Hughes married in 1967

Question: How long was they married?
Self-contained rewrite: How long was Robert Hughes the critic married?