Usually takes about two hours every two weeks, but I figure we’d have lost that time in offline code reviews anyway. I’ve had people point out that I have a small team. They have a point, I’m not sure how this would scale to a large team—but maybe if a team is too large to review their code together they could be split into smaller groups.
Also, I think these help replace what might have been other meetings as well. Sometimes product people like to sit in and listen so they know exactly what's being released--I don't think they'd ever participate or get much value from a normal code review.