Changed, being dull, given a time inside (7)
I believe the answer is:
mutated
'changed' is the definition.
(mutating is a kind of changing)
'dull given a time inside' is the wordplay.
'dull' becomes 'muted' ('muted' can be a synonym of 'dull'**).
'given' indicates putting letters inside.
'time' becomes 't'.
'inside' means one lot of letters goes inside another.
'muted' placed around 'a' is 'mutaed'.
'mutaed' placed around 't' is 'MUTATED'.
'being' is the link.
(Other definitions for mutated that I've seen before include "Made different" , "made changes" , "Changed form" , "Changed (biologically)" .)