taking visa intervie late at chennai

[kasede]

Hai
Iam a first time h1b holder and my appointment letter says my date of joining the employment is on oct 1 or after the visa is approved.i have blocked nov 19 in chennai consulate.what doubt i have is will the vo ask me why u r taking the interview after one and half months of the joining date.should i have to produce any supportive documents for this.
thanks in advance