That doesn't answer my question :-) Are you all regularly having terrible problems that need in-depth discussion? Are you all celebrating every success with its own party? Are your processes so wildly off the mark that you have to change everything every sprint? Is there something else you do in your retrospectives that I don't? For my current team (also around 10-12 devs, 2 week sprints) it's:

- what went well? we completed most/all of our tasks, cracked a tricky problem, received good feedback from somewhere - let's say 5-10 minutes of celebration

- what didn't go well? maybe a task was more difficult than expected, some new requirement added unexpected difficulties, some third party something didn't perform as expected - 10-15 minutes of commiseration and discussion, maybe more if there's something complicated, perhaps that requires further action

- what would you do differently? unless there are some procedural problems, I would expect almost nothing here; maybe someone has some new ideas about how to improve something, perhaps some aspect of the project isn't running as smoothly as it could - 5-10 minutes maybe

So about thirty minutes max across the whole team, usually less. What secret magic are we missing out on? Six hours??

Six hours is longer than I would use for a regular retrospective, but 30 min is very short. The format you’ve described is fairly shallow. Check and Derby and Larsen’s Agile Retrospectives for ideas about what you might be missing.