I should be in now he's in the chair (9)
I believe the answer is:
president
'chair' is the definition.
(eg chair or president of a board)
'i should be in now he's in' is the wordplay.
'should be in' is an insertion indicator.
'now' becomes 'present' (the present time).
'he' becomes 'd' (I can't explain this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'i' placed into 'present' is 'presient'.
'presient' enclosing 'd' is 'PRESIDENT'.
'the' is the link.
Can you help me to learn more?
(Other definitions for president that I've seen before include "American leader" , "Head of US company - tried pens (anag)" , "Head, of a republic say" , "Our head of state has a strange red instep" , "Grant perhaps" .)