i want to spend an hour at the gym

It's not about the time as much as how you maximize the time. Cardio in the form of a bike or elliptical is good but you'll burn more calories doing full body workouts. Most gyms have those types of classes. But making sure to work weight training in is super important. The trick there, if you're trying to shed some weight, is making sure you keep your heart rate up. So you want to try to keep the 'rest' periods short between sets and exercises.