Decided in advance (3,3,5)
I believe the answer is:
cut and dried
'decided in advance' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cut and dried that I've seen before include "to have it [HAIRSTYLE] so treated?" , "Already decided" , "how hair should be?" , "arranged" , "Completely settled" .)