Contents of a debrief
When I think about doing a session debrief, I always include reviewing the session notes, having the tester tell a story of their testing, and me asking questions about what was/wasn't tested as part of the debrief. So a typical debrief for an experienced tester on my team might take five to ten minutes. For a junior tester, it might take ten to twenty minutes. If I'm doing them well (and that's a big if), than they take time. Ideally both of us (the tester and myself) are getting something out of the debrief.