Some conducting jobs are a matter of measured growth over a number of rehearsals, towards an eventual artistic performance. You collaborate to discover the perfect performance for this ensemble, in this moment, on this piece.
Other conducting jobs are essentially parachuting in, quickly and effectively teaching notes and rhythms while ensuring that the ensemble gets a sense of sound and unity in too-little time. You have to set concepts quickly and build from basic concepts to confident singing.
Both have their place, and both require different skills. Most importantly, when she parachutes in, the conductor must have a clear, easily presentable sense of the pieces – both musically and in terms of vocal tone. It is only with that knowledge that the conductor can help the singers move quickly to musicality.