This time doctor welcomes new arrival (6)
I believe the answer is:
advent
'arrival' is the definition.
(advent is a kind of arrival)
'this time doctor welcomes new' is the wordplay.
'this time' becomes 'ad'.
'doctor' becomes 'vet' (vet is a kind of doctor**).
'welcomes' is an insertion indicator (in sense of 'invites in').
'new' becomes 'n'.
'vet' going around 'n' is 'vent'.
'ad'+'vent'='ADVENT'
(Other definitions for advent that I've seen before include "Arrival (with calendar?)" , "Period in the Christian calendar" , "Period before Christmas" , "It's a-coming in December!" , "Christian season" .)