Group taking a long time to deliver parcels (8)
I believe the answer is:
packages
'parcels' is the definition.
('package' can be a synonym of 'parcel')
'group taking a long time' is the wordplay.
'group' becomes 'pack' (pack can mean a group of things).
'taking' is a charade indicator (letters next to each other).
'a long time' becomes 'ages' (ages can mean a very long time).
'pack'+'ages'='PACKAGES'
'to deliver' acts as a link.
(Other definitions for packages that I've seen before include "Parcels" , "Wraps up good preparatory toposting" .)