Group taking long time dressing (7)
I believe the answer is:
bandage
'dressing' is the definition.
(dressing for a wound)
'group taking long time' is the wordplay.
'group' becomes 'band' (band can mean a group of people).
'taking' means one lot of letters go next to another.
'long time' becomes 'age' (an age is a period of time).
'band'+'age'='BANDAGE'
(Other definitions for bandage that I've seen before include "Injury protection" , "Cloth to cover injuries" , "First-aid item" , "Wrapping for wound" , "Wound binding" .)