Excuse expert fabricated ahead of time (7)
I believe the answer is:
pretext
'excuse' is the definition.
(a pretext is an excuse or pretence)
'expert fabricated ahead of time' is the wordplay.
'fabricated' indicates an anagram.
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'time' becomes 't' (abbreviation).
'expert' with letters rearranged gives 'pretex'.
'pretex'+'t'='PRETEXT'
(Other definitions for pretext that I've seen before include "Excuse for an action" , "False reason, guise" , "Ostensible justification" , "False excuse" , "Alleged reason" .)