Holiday sailor can take on land, or else have at sea (5,5)
I believe the answer is:
shore leave
'holiday sailor can take on land' is the definition.
(sailor's leave on land)
'or else have at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'or'+'else'+'have'='orelsehave'
'orelsehave' is an anagram of 'SHORE-LEAVE'.
(Other definitions for shore leave that I've seen before include "Time off for sailors in port" , "rest of the crew" .)