Eventually book on time (2,4)
I believe the answer is:
at last
'eventually' is the definition.
(thesaurus)
'book on time' is the wordplay.
'book' becomes 'atlas' (atlas is a kind of book**).
'on' says to put letters next to each other.
'time' becomes 't'.
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "None too soon" , "Where cobbler located" , "Finally, after a long wait" , "Where a snob worked" , "Finally, having waited a long time" .)