Most imprecise, loses time, digesting nothing (7)
I believe the answer is:
loosest
'most imprecise' is the definition.
('loose' can be similar in meaning to 'imprecise')
'loses time digesting nothing' is the wordplay.
'time' becomes 't'.
'digesting' means one lot of letters goes inside another.
'nothing' becomes 'o' (looks like zero - 0).
'loses'+'t'='losest'
'losest' going around 'o' is 'LOOSEST'.
(Other definitions for loosest that I've seen before include "most relaxed" , "most unstable" .)