Thirty minutes covers both
Almost everything written about Campbell and meditation stops at the meditation. His own dose statement does not. Thirty minutes twice a day, he writes, is enough to accomplish both the meditation and the examination of your choices — take more if you wish, but much more is not necessary.
Both. The sitting is one part; going back over your own choices and the motives under them is the other, and it gets equal billing in the only sentence where he specifies how much time to spend.
The review is simple and it is not a confession. You look back over the day's choices, find the intent that was actually driving each one, and adjust — towards more giving and more caring, and away from what serves you. That is all. No tallying, no penance.
Two rules about when. Not during the sit — analysis is exactly what kills a meditation, and he is unambiguous that judging and assessing belong afterwards. And not in a rush. The review works because the mind is quiet when you do it, which is why it belongs immediately after sitting rather than in a spare five minutes on a train.
The measure of whether any of this is landing is not how the review feels. It is whether anything about how you actually behave has changed — because in his account, understanding that stays intellectual is not understanding yet.
The thirty-minute figure and the phrase covering both are his; the shape of the review is our reading of what he describes.