Mid-January on patio, drunk, is heaven (6)
I believe the answer is:
utopia
'is heaven' is the definition.
(a utopia is a perfect place)
'mid-january on patio drunk' is the wordplay.
'mid' says to take the centre (mid- can mean the middle of something).
'on' is a charade indicator (letters next to each other).
'drunk' indicates anagramming the letters.
The central letter of 'january' is 'u'.
'patio' is an anagram of 'topia'.
'u'+'topia'='UTOPIA'
(Other definitions for utopia that I've seen before include "More's ideal world" , "Imaginary ideal place" , "Place of ideal perfection" , "of limited interest to G&S" , "A perfect place according to Thomas More" .)