Almost failing to start ahead of schedule (5)
I believe the answer is:
early
'ahead of schedule' is the definition.
(I've seen this before)
'almost failing to start' is the wordplay.
'almost' becomes 'nearly' ('nearly' can be a synonym of 'almost').
'failing to start' means to remove the first letter.
'nearly' with its initial letter removed is 'EARLY'.
(Other definitions for early that I've seen before include "Beforehand" , "Forward" , "New-season" , "before anyone else?" , "with time to spare?" .)