I don't have any scientific advice or information to offer, but I'm doing almost the same thing 2 hrs on the trainer in front of the TV 3-4 times per week. A couple of days ago I did a 30 mile ride (a real ride, outside even!) and it took around 2 hours. Judging on how I felt only, the 'real ride' was less of a workout than 2 hours on the trainer, so I'm thinking that the time on the trainer is a (monotonous and terrible, but) pretty good workout.