Best time to work dye into dried grass (6)
I believe the answer is:
heyday
'best time' is the definition.
(I've seen this before)
'work dye into dried grass' is the wordplay.
'work' indicates an anagram.
'into' means one lot of letters goes inside another.
'dried grass' becomes 'hay' (I've seen this in another clue).
'dye' is an anagram of 'eyd'.
'eyd' inserted inside 'hay' is 'HEYDAY'.
'to' is the link.
(Other definitions for heyday that I've seen before include "Period of greatest success and popularity" , "Period of greatest vigour" , "The time of greatest success or prosperity" , "Prime time?" , "Period of one's greatest success" .)