Citra is best used as a flavor/aroma hop. It is also expensive and in high demand, so to use it as a bittering hop, where no aroma or flavor is really produced, is kind of a waste.
using the same amount of hops (3oz cascade, 2oz citra), I would do the following as a schedule. I like to add them all at the end for max aroma/flavor:
1oz Cascade 60min
1oz Citra 0min (20min hop stand)
1oz cascade 0min (20min hop stand)
1oz Cascade Dry Hop (5-7 days)
1oz Citra Dry Hop (5-7 days)
by doing the 20min hop stand for the 0min additions, you get both aroma and flavor from one hop addition!