Tie many in a knot whenever you like (3,4)
I believe the answer is:
any time
'whenever you like' is the definition.
(I've seen this before)
'tie many in a knot' is the wordplay.
'in a knot' indicates anagramming the letters.
'tie'+'many'='tiemany'
'tiemany' with letters rearranged gives 'ANY TIME'.
(Other definitions for any time that I've seen before include "at one's disposal night and day" , "Whenever you like" .)