Hm, realistically, as much weight as you need to lose. It depends on how much you can change your diet. You need to think about changing your diet/exercise habits permanently. "Dieting" does jack ****** for you. You simply lose the weight, go back to your old life, and regain it.
Some pointers:
Exercise time: when you need to take a break from whatever it is you are doing (I'm assuming you don't work in construction), take a brisk walk around the office or around the block. Come back to your office, do some crunches, pushups or modified pushups, and bodyweight squats. (google these terms if you dont understand them). It will take all of 5-10 minutes, and it will be great exercise. If you do this 2-3 times a day when you need a break, you'll be fitting in good exercise. On the weekends do something serious like go for a long bike ride or something. Like magic, you're working out every day for at least 30 minutes a day.
Diet: Look at what you are eating. Keep a log of what you are eating, and the portions. Keep a log of how you feel afterwards. Do this for a week. At the end, count the estimated number of calories you think you consumed. Now, design a new "mealplan" for your next week. Cut out things like: burgers, fries, shakes, soda, etc. I'm not saying don't go to burger king, I'm saying go to burger king, order the grilled chicken sandwich, a salad, and a water. You want to be consuming approximately the same number of calories you were before, but you want to be consuming more HEALTHY calories:
complex (grain) carbohydrates
lean protein
some (minimal) fat
fiber!
and less unhealthy calories:
fat
saturated fat
simple carbohydrates (sugars)
This meal planning will actually make you LESS hungry, because protein, fiber, and complex carbs will keep you full for much longer than simple carbohydrates and fat will. Do this meal planning on a Sunday, on a week to week basis. If you find you get tired of say, eating salads, this allows you to change the plan up.
The idea is not to drastically change your diet from fast food to tofu and bean sprouts. The idea is to make small changes to your lifestyle which are completely livable in the long term, and will make you gradually lose weight.
edit: I'm not suggesting all you eat is fast food, I was just using it as an example, because you said you have no time for your diet, which means to no time to cook, no time to exercise, etc.
Realistically, you should be able to get down to or just above your "ideal" weight. Next time you go to the doctor, make sure and ask him about weight loss, ideal weight, etc. They will also have plenty of good pointers to give you.