If you don't care about muscle at all, can do cardio 6 times a week, 40min per day. That's like HIIT(High Intensity Interval Training), jog until you're tired, then walk, repeat etc. Leave 1 day to rest. If that is too much just reduce the days but at least 3 per week minimum, 30min duration per day. Start much slower of course if you haven't been exercising at all, body +muscles needs to get used to it first.

Most importantly however, is diet. To lose weight, calories out must be > calories in. So calories out must come from diet + exercise to be the fastest. Of course diet plays the biggest factor as 1 chocolate bar can waste 1 whole hour's effort of cardio, for example. Do not starve yourself however, as your body will slow its metabolism to preserve fat and burn muscle. Have to lose weight slowly, 1 pound per week is recommended if I'm not wrong. That's about 500 calories deficit per day. 3500 calories gone = 1 pound of fat gone.

I tried to read whether you can preserve/gain muscle while trying to lose weight from a lot of sites, but I think most said cannot. To gain weight, you need more calories than normal(especially protein) while to lose weight, you need less calories than normal. But I still do squats/pushups/bicep curls while doing heavy cardio anyway, since I have lots of free time. If you do try to do both, make sure you weight lift first before cardio, not the other way around.

Note: this is only what I learned from reading other people's experiences, may be wrong.