Map book arrives on time in the end (2,4)
I believe the answer is:
at last
'in the end' is the definition.
('at last' can be a synonym of 'in the end')
'map book arrives on time' is the wordplay.
'map book' becomes 'atlas' (I've seen this before).
'arrives on' means one lot of letters go next to another.
'time' becomes 't'.
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "Finally, ultimately" , "Finally, after much delay" , "Finally, having waited a long time" , "None too soon" , "working as a cobbler?" .)