Yes. You add pranayama in addition to meditation. Consider the 8 limbs of yoga. first is a good ethical lifestyle. Next is asana. Then pranayama. Then withdrawal of external stimulation, then concentration, meditation, and finally the super conscious state.
So if you want to see the subtler effects of the pranayama practice, you can practice meditation afterwards. But considering your schedule, I would probably do the guided meditation, then walk, then pranayama. :)
And also Id recommend playing around with try it. Maybe try the walk first then pranayama then meditate. Or do pranayama before the guided meditation then walk. See where it best intuitively fits for your goals.