Geographer's helper on time, finally (2,4)
I believe the answer is:
at last
'finally' is the definition.
(synonyms)
'geographer's helper on time' is the wordplay.
'geographer's helper' becomes 'atlas' (reference work used by a geographer).
'on' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'atlas'+'t'='AT LAST'
(Other definitions for at last that I've seen before include "Where cobbler located" , "working as a cobbler?" , "Where a snob worked" , "Finally, having waited a long time" , "None too soon" .)