I got ~ 2.5 days advance notice to facilitate the retrospective. Given other prior commitments, I had ~ 6 hours to prepare.
The retrospective was scheduled for 2 hours (teleconference) and I was told that the team (sponsors and development) didn't find retrospectives particularly useful i.e. Received benefit < Time invested
So my challenge was to make this retrospective useful or at least tilt the scale towards it being useful.