To contrast, when I made my flanders red I fermented first with S-04 to get down to 1.016. Then, I racked to secondary and pitched the roselare blend.
However, I was merely looking for something less sour than Rodenbach Grand Cru, from what I understand if you want more sourness, it is best to do what flyangler18 suggested. However, if you are looking for something more along the lines of Rodenbach Classic, like I was, I would suggest following my method.
The time in the carboy remains the same for both beers in my opinion.