Yes...if it is combined with a healthy low-calorie diet as well.
Riding a bike for that amount of time is only going to burn about 300 calories. This amount of calories burned will be much lower than the calories you burn at your resting rate or simply walking around all day. The lesson here is that exercise has many benefits, but don't "reward" yourself for exercising by eating a bigger meal because the actual calories burned will be so small in comparison with what your body burns anyways.
For long-term weight loss, you may want to add in some type of resistance or strength training. This will help you build muscle which will increase the number of calories you burn at a resting rate (e.g. when you're kicking back watching television). It is also important because some of the weight you lose will be muscle which is counterproductive because this lowers your metabolism. Muscle loss is one of the main reasons people hit walls in their weight loss programs and then put weight on much easier once they stop their diet.
The most important aspect (far and away) is healthy eating. Use some online calculators to try to determine your BMR (type in BMR calculator into a search engine) and then shoot for taking in about 500 calories less than what it says your body burns per day. This, combined with exercise, will help you get towards a healthy 2lbs of fat loss per week.
Good luck.

I think that is good enough. If you want to speed up your weight loss, though, I think we should add various exercises in order to develop your whole body and not just your legs. For example, do different exercises everyday. You can do cycling for day 1, swimming for day 2, jogging for day 3, muscle development for day 4, and then go back to cycling for day 5 and so on. This would increase your fat loss. Otherwise, your exercise plan is formidable enough. Im jyst making suggestions. Anyway, good luck!

It will help, but its hardly formidable.....
3 hours a day maybe.

Perhaps if it were also paired with a few other small excercises crunches, situps, etc. As well as healthy eating habits and some stretching you have yourself a good start to a weight loss plan, or should I say, lifestyle.

Well, if you haven't done that before then it should help you lose weight. If you already are doing it then you will hit a plateau and need to do other things to ensure you keep progressing.
It also depends on your diet. I know a lot of people that spend hours a week on exercise bikes and are still overweight.
You only lose weight if you eat less calories than you expend. So increasing exercise + eating less calories is the only way to have a "formidable" weight loss program.
Lastly, most people actually want to be toned up (not just skinnier). So you will need to do some resistance training as well.

Diet is the prime determinant of weight loss. The biking should help though, good for cardio as well.

You should also be following a healthy eating plan. If possible find out how high your heart rate should be to maximise the weight loss (usually worked out by age and weight) Good luck :-)

It's one part of a weight loss plan. Cardio is very important, but you don't need to do it every day. 3-5 times a week for 30-45 minutes is better, otherwise you are overworking it and you will stop losing weight because you are no longer "shocking you body." Remember to switch up your routine every 6 weeks otherwise, as mentioned before, your body gets used to the cardio you are doing and will depend on it. You wont gain wieght, but you won't lose any either. By, let's say, doing a run instead one day or going for a swim, you "shock" your body and it starts to burn more.
Also, make sure that you are sweating and that your cardio is at a "fat burning zone." Most machines have a chart indicating where that is depending on your age and weight.
You can also incorporate weights into your routine, but you don't have to. If you are looking to shrink, cardio is enough (but if you are obese your skin may sag). Eventually you will want to incorporate a weights routine. I lost 40lbs before I started doing weights, so I shrunk and then built muscle rather than getting bulky.
Another key element to weight loss is diet. Diet and exercise go hand in hand. You need both if you want to see serious results. Simply eat from all the food groups in the appropriate portions. Don't forget to allow yourself the occassional treat (i.e. an ice cream at the end of the month,or going out for a dinner after you drop 10 ls) to keep you going. Remember that bieng healthy is about a healthy lifestyle and not a quick fix weight loss plan.

You should actually do 5 sessions a week, for at least an hour per session, for optimal cardiovascular health and fitness.