Beast wasted time, in the most optimistic view (2,4)
I believe the answer is:
at best
'the most optimistic view' is the definition.
(I've seen this before)
'beast wasted time in' is the wordplay.
'wasted' indicates anagramming the letters.
'time' becomes 't' (abbreviation).
'in' means one lot of letters goes inside another.
'beast' with letters rearranged gives 'abest'.
'abest' enclosing 't' is 'AT BEST'.
(Other definitions for at best that I've seen before include "Making every allowance" , "Under optimum conditions" , "In the optimum situation" , "In the most optimistic scenario" , "In the most favourable outcome" .)