For a good, realistic, sustainable amount of weight loss, we generally target a calorie deficit of about 500kcal/day (a bit higher if you have a very high bodyfat %, a bit lower if you already have a low bodyfat%), which is about 45-60min worth of continuous exercise, depending on intensity.
Of course, as I've discussed in the training for fat loss sticky, strength training 2-3 times a week is more important for body composition than cardio -- it can be set up to burn just as many calories as you would in a cardio session, and unlike cardio it preserves lean body mass, so the weight you lose is actually coming from fat.