Crucial stage or turning point (6)
I believe the answer is:
crisis
This clue is a double definition.
'crucial stage' is the first definition.
(I've seen this before)
'turning point' is the second definition.
(I've seen this before)
(Other definitions for crisis that I've seen before include "Difficult moment" , "crucial period" , "Emergency - decision time" , "Climax, breaking point" , "Turning point in disease" .)