"Dancing With the Stars" begins its next season on September 22nd. On the Monday and Tuesday of that week, there will be a two-hour performance episode (the Monday episode begins at 8 PM while the Tuesday episode begins at 9 PM). The first results show of the season airs that Wednesday at 8 PM.
"Opportunity Knocks" premieres on September 23rd at 8 PM, preceding "Dancing With the Stars".
Source: The Futon Critic