Time enough to set, or harden (7)
I believe the answer is:
toughen
'harden' is the definition.
(thesaurus)
'time enough to set' is the wordplay.
'time' becomes 't'.
'to set' indicates an anagram (instruction to set the letters).
'enough' with letters rearranged gives 'oughen'.
't'+'oughen'='TOUGHEN'
'or' acts as a link.
(Other definitions for toughen that I've seen before include "Increase stiffness" , "Make more resilient" , "Make strong and durable" , "Make stronger and hardier" , "Make more robust" .)