i am a reapplicant with finance background. I could recall last year one mainland china applicant in CD submitted his part-1 back in Sep/Oct. Before his submission of part-2 in R2 (say Jan), he received an invite in Nov or so.
I actually asked the adcom specifically in one info session if the interview invite had to come after part-2 submission. The adcom said no and they would proceed the interview invite right after part-1 submission.