Yes and no.
In many countries consular officer allow them. In Bangladesh it is not allowed.
So here it is. You will receive the Second letter - Interview date from the KCC 4 - 6 weeks before the scheduled interview date. That day you will pay the non refundable visa fees and you will face the interview. There they will check your personal, education, medical, police report, affidavit of support and other documents.
So some people say they are not ready with the documents and want to postpone the interview date.
To this you must contact the consular officer as mentioned in their official web site and do as required.
But for Bangladesh people it is clearly stated that they will loose their chance if they didn’t appear for the interview on that particular day.

Also take note,
There are only a limited number of visas available.
And it is issued as first come first served basis.
If you reschedule your interview you may loose the chance of getting a visa if other eligible people went to the interview before you and the visas are over.
DV Lottery 2009 visa interview session will start in October 2008 and will close on midnight 30th September 2009. After this date the dv lottery winning will not be valid for to obtain a visa or to change status.