It's right to discuss at tedious length … (4,2)
I believe the answer is:
bang on
I believe this clue is a double definition.
'it's right' is the first definition.
'to discuss at tedious length' is the second definition.
(Other definitions for bang on that I've seen before include "Absolutely right - sounds noisy" , "Informally and absolutely accurate; it's explosive" , "Exactly right - sounds noisy" , "Absolutely right, informally explosive" , "with great accuracy" .)