I’m not familiar with the training plan in particular, but I am familiar with Scott J’s swimming recommendations for weight-bearing athletes.
These sessions are not intended as workouts. The intensity is very low, not to create fitness, but to speed recovery. Because recovery is the focus, I suspect it’s best to have a swim session between two harder sessions or as the last session of the day.
Again, I’m not familiar with Luke’s training plan, so feel free to correct me if I’m mistaken.