I have been in situations many years ago when I was very pressed for time, and was lucky to get in 3 days a week, and was lucky to have an hour or so. Nowadays, I never go over an hour on the weights (not counting cardio) 4 days a week anyway even with a home gym and more time to train.
What I would do would be to divide the body up into back/bis on one day, chest/delts/tris 2 days later, and legs 2 days after that. Basically either a Mon-Wed-Fri or Tues-Thurs-Sat split, with two whole days off after legs.
I'd do 30-45 minutes on the weights, then immediately use the remaining 15-30 minutes of cardio. Heavy weights, compound exercises, relatively little rest between sets. Squats, Deads, Bench press, bent rows, pullups, dips, leg press, military press, calf raises, etc. 8-15 reps on most sets of most exercises. Try to do at least 12-15 sets on the weights during those 30-45 minutes.
Depending upon how healthy you are (cardiovascular, blood pressure, etc), exactly how big and lean you are now, and whether you'd want to be more "jacked" looking rather than extremely lean and "fit" with just some muscle, you might or might not consider temporarily just focusing on the weights for that hour you have 3 days a week if your shortage of time is only temporary.
I've personally always leaned more towards training for size and strength and using a reasonable diet and a little cardio to maintain a reasonably low bodyfat. I've never been one to have or even shoot for extremely low bodyfat, but everyone is different.
Either way, some weight training with reasonably heavy weights and basic compound movements will go a long way towards maintaining muscle size while dropping bodyfat. Maintaining as much muscle as possible will help keep your body composition where it needs to be - more muscle burns more calories around the clock. A good diet will be key for most people when getting extremely lean.
