Layer shifted in advance (5)
I believe the answer is:
early
'in advance' is the definition.
(similar in meaning)
'layer shifted' is the wordplay.
'shifted' indicates an anagram.
'layer' with letters rearranged gives 'EARLY'.
(Other definitions for early that I've seen before include "This bird gets the worm" , "Advanced" , "Prematurely" , "Infancy, when Wordsworth had 5 across of 5 down" , "Before the usual time" .)