If you want to take something up, now's the time to choose (5)
I believe the answer is:
adopt
'if you want to take something up now's the' is the definition.
I can't tell whether this defines the answer.
'time to choose' is the wordplay.
'time' becomes 'ad'.
'to choose' becomes 'opt' (I've seen this before).
'ad'+'opt'='ADOPT'
Can you help me to learn more?
(Other definitions for adopt that I've seen before include "Espouse" , "Choose as one's own" , "Start to wear" , "choose as candidate" , "Take up, follow" .)