Hold on a minute there - do you mean Cistus (shrub) or do you mean Helianthemum (rock rose)?
If you mean Cistus (as in Peggy Sammons, Corbariensis, etc.) then they don't like being pruned at all, so you have to restrict yourself to removing dead and damaged wood in Spring.
If you mean Helianthemum, these should usually be clipped in August, but too late now, so you'll have to clip them back after flowering in Spring/early summer.