In the first few years of Idol, the performance shows stepped down from 2 hours to 90 minutes to 1 hour fairly quickly, and the results shows were 30 minutes. Now those were the days!
We only watch on DVR and it takes about 35 minutes to watch a 2 hour show that way by the time you skip all the commercials, the "coming up after the break" previews, and the silly blather. We usually just stick with the performances and the actual results. The results shows take only like 15 minutes to watch because half those episodes are clips from the show aired the previous night!