Johnny-come-lately is on time, come over (9)
I believe the answer is:
arriviste
'johnny-come-lately is on time come over' is the definition.
I can't tell whether this defines the answer.
'is on time come over' is the wordplay.
'on' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'come' becomes 'arrive' (synonyms).
'over' indicates putting letters inside.
'is'+'t'='ist'
'ist' going within 'arrive' is 'ARRIVISTE'.
Can you help me to learn more?
(Other definitions for arriviste that I've seen before include "Ambitious and self-seeking person" , "Social climber" , "Ambitious self-seeker" , "Upstart" , "Parvenu" .)