Eat dinner with time unusually vague (13)
I believe the answer is:
indeterminate
'vague' is the definition.
(I've seen this before)
'eat dinner with time unusually' is the wordplay.
'with' is a charade indicator (letters next to each other).
'unusually' indicates anagramming the letters.
'eat'+'dinner'+'time'='eatdinnertime'
'eatdinnertime' is an anagram of 'INDETERMINATE'.
(Other definitions for indeterminate that I've seen before include "Having no fixed value" , "uncertain result?" , "Unfixed, uncertain" , "Not exactly defined" , "Unspecified" .)