Terrible about time, to be frank (6)
I believe the answer is:
direct
'frank' is the definition.
(similar in meaning)
'terrible about time' is the wordplay.
'terrible' becomes 'dire' (synonyms).
'about' becomes 'c' (abbreviation for 'circa').
'time' becomes 't'.
'dire'+'c'+'t'='DIRECT'
'to be' acts as a link.
(Other definitions for direct that I've seen before include "Frank; undeviating" , "Take charge, of a film perhaps" , "Aim; straight" , "Supervise; unambiguous" , "Immediate; organise (e.g. play)" .)