During school time, nine of the Romans mingle (8)
I believe the answer is:
intermix
'mingle' is the definition.
(I know that intermix is a kind of mingle)
'during school time nine of the romans' is the wordplay.
'during' becomes 'in' (e.g. during February means in February).
'school time' becomes 'term' (term time).
'nine of the romans' becomes 'ix' (nine in Roman numerals).
'in'+'term'+'ix'='INTERMIX'
(Other definitions for intermix that I've seen before include "Mingle" , "Stir" , "Blend together" .)