With great skill, branch line's put together within a year (7)
I believe the answer is:
adeptly
'with great skill' is the definition.
(I've seen this before)
'branch line's put together within a year' is the wordplay.
'branch' becomes 'dept' (abbreviation for department).
'line' becomes 'l' (used when specifying particular lines from a poem).
'put together' means one lot of letters go next to another.
'within' indicates putting letters inside.
'a year' becomes 'ay' (I can't explain this - if you can you should believe this answer much more).
'dept'+'l'='deptl'
'deptl' inserted within 'ay' is 'ADEPTLY'.
Can you help me to learn more?
(Other definitions for adeptly that I've seen before include "Showing skill" , "Skilfully" , "Adroitly" , "with great skill" , "How experts act" .)