possibilities...depending on your health and fitness level
You may need to pick up a lot of little activities during the week days and but have dedicated exercise time on the weekends. On the weekends, if you work up to it you could do a different and intense cardio and strength training workout each weekend day (so that would be 2 big workouts two days in a row--just do not do the same thing each day) plus maybe something recreational such as bike ride, squash or racket ball (often a bit pricey for court time) , dancing, yardwork, martial arts later in the day for 30 to 60 minutes. This may take a long time to work up to --age injuries from the past and fitness level and your basic make up are factors. If you jump in too fast, it will also take ou a long time to recover. So that would be the end point, not the initial step forward.
Remember there are more opinions about fitness training than any other human human activity and you can spend a lot of time avoiding the "good" just to find the "best". The main thing is to find something you can do without injury, vary it to prevent injury and to deliberately confuse your body, and just do it. If you have not worked out or are over a certain age (12?), had an injury, or whatever, get a good physical before you start from your doc and consider booking a trainer or joining a class at appropriate level.
Weekdays: fit in a lot of little things 2 to 5 to 10 minutes each--maybe aim for 6 of them--make a list and check them off. Circumstance might dictate your actual choice.
1. I can't do this but I know someone whose fitness is such that he can get on the treadmill, warm-up in in 2 minutes and get 8 minutes of cardio-really intensely. He cools down by racing around his apartment tidying up. He does this twice a day. His wife loves the tidying and his adorable physique. He plays around with 20 pound barbell while on the phone at work and also at home and uses the hand strength resistance squeeze thing in the car.
2. Don't have a treadmill? how about an old tire in your living room or garage and build up to hitting it 100x with a light weight sledge hammer, hang a speed bag somewhere where in your place, or can you jump rope anywhere?
3. Can you take stairs at work? Can u do that a couple of times a day?4.
4. Can you sit on a ball as a chair? Hard to get the appropriate height but very effective.
5. Can you put a pedal device under your desk? Often awkward to sustain but might be a good warm up before mental work.
6. How about a stand up desk, at least part of the time7. ?
7. If your joints are good, some people feel that slow and very heavy lifting is aerobic. Like 4 rep max on a major muscle group, 10 seconds in each direction, no momentum and you can even take the negative more slowly for 12 to 15 seconds (that's the part where its is easy to let gravity take ove, just go super slowly). Find three exercises you can do with a heavy bar o plates and do them twice a week. See book Power of Ten. Not okay for arthritic joints however.
8. If you are a man ( or a women whose strength readily develops) and, your potential for fast strength development will give you a muscle advantage that can enable you to do some intense body weight work outs that will be aerobic and take little time and keep your muscles in great shape: try alternating 1 minute of pull ups on a bar (carefully) installed in your door way with mountain climbers on the floor, do one minute of each! Next day, do alternating push ups and burpees.
9. Before bed 5 minutes of stretching/ yoga, isometric core exercises like plank and side plank, or wall sit with a weight in your lap, an 8" play ball between your legs and a raised dumbell in your hand which you gently switch back and forth to the other hand. You can rotate through these by the week.
If you're just beginning: bring a smoothie for lunch and drink it while you take a walk or stair climb, and every hour or so, rise from setting to standing 5 times while pulling a stretch band over head. Wear a pedometer and aim to increase number of steps by 5% every week. If you have a good back, you could add a weighted vest to your walking but I would not do it everyday since it can throw off your gait and probably cause spinal stenosis in later life. Let me know if you find a good pedometer that you can recommend--in fact, your next action could be to buy the pedometer and a stretch band and make a chart. No bog investment and not much time either. Good luck and tell us how to make it all work.