Tea and dinner-time strangely uncertain (13)
I believe the answer is:
indeterminate
'uncertain' is the definition.
('indeterminate' is associated in meaning with 'uncertain')
'tea and dinner-time strangely' is the wordplay.
'and' says to put letters next to each other (I've seen this in other clues).
'strangely' indicates an anagram.
'dinner'+'time'='dinnertime'
'tea' after 'dinnertime' is 'dinnertimetea'.
'dinnertimetea' anagrammed gives 'INDETERMINATE'.
(Other definitions for indeterminate that I've seen before include "Not exactly defined" , "uncertain result?" , "Unspecified" , "Unfixed, uncertain" , "Having no fixed value" .)