Mark in time a new dawn, initially reforming nation (9)
I believe the answer is:
andantino
'mark in time' is the definition.
(tempo mark in music)
'a new dawn initially reforming nation' is the wordplay.
'initially' indicates taking the first letters.
'reforming' indicates an anagram.
The initial letters of 'new dawn' is 'nd'.
'nation' with letters rearranged gives 'antino'.
'a'+'nd'+'antino'='ANDANTINO'
(Other definitions for andantino that I've seen before include "Slightly faster than walking pace (mus.)" , "At a light moderate pace (music)" , "at a gentle pace" , "Musical tempo - ain't donna (anag)" , "Musical piece" .)