Schedule repair of adrenal cortex, to start with (8)
I believe the answer is:
calendar
'schedule' is the definition.
(calendaring is a kind of scheduling)
'repair of adrenal cortex to start with' is the wordplay.
'repair of' indicates anagramming the letters (I've seen 'repaired' mean this).
'to start with' suggests taking the first letters.
The first letter of 'cortex' is 'c'.
'adrenal'+'c'='adrenalc'
'adrenalc' is an anagram of 'CALENDAR'.
(Other definitions for calendar that I've seen before include "dates listed" , "Almanac" , "Year chart" , "Chart of times" , "series of dates" .)