Even repair inventions on time, most in advance (8)
I believe the answer is:
earliest
'most in advance' is the definition.
('early' can be similar in meaning to 'in advance')
'even repair inventions on time' is the wordplay.
'even' indicates alternate letters (even-numbered letters are used).
'inventions' becomes 'lies'.
'on' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
The alternating letters of 'repair' are 'ear'.
'ear'+'lies'+'t'='EARLIEST'
(Other definitions for earliest that I've seen before include "With the least delay" , "First occurring" , "Furthest back in time" , "Very first in a sterile manner" , "Soonest" .)