It took me 16 months to lose 90 lbs. My biggest hurdles were 2 plateaus that lasted a couple of weeks. The sooner you tackle a plateau, the easier it will be to break it.
The first I only had to add some nighttime cardio - a 30 minute walk at night did the trick. The second I had to add 400 calories to my daily requirements because I was now burning so many calories that I stopped losing weight.
When you hit your first plateau, you will find a lot of help here at SparkPeople. Don't just accept it - try to break it!