Slipped away unusually pleased (7)
I believe the answer is:
elapsed
'slipped away' is the definition.
('elapse' can be a synonym of 'slip away')
'unusually pleased' is the wordplay.
'unusually' is an anagram indicator.
'pleased' with letters rearranged gives 'ELAPSED'.
(Other definitions for elapsed that I've seen before include "Expired" , "Pleased to have passed" , "slipped away" , "Pleased (anag.)" , "Passed, of time" .)