i don't think people with no time to exercise has the luxury to focus on specific parts of the body. if i'm such person, i'd buy a skipping rope, a pull-up bar and just do some bodyweight exercises + skipping (cardio) in my room every morning/before bed.

i think it depends on individual. my routine now is to go to the gym at around 10pm and works out til 12am when the gym closes. i'll take a quick shower once i reach home and jump on bed to sleep afterwards.