Either of the following sounds okay:
Can we postpone the interview a little bit?
Can we postpone the interview a little?
If it's the day of your interview, I would interpret "a little bit" to be at most a few hours. If you wanted to delay until tomorrow, I'd just say:
Can we postpone the interview until tomorrow?
Having said that, I would expect at least 24 hours notice if a candidate wanted to reschedule. I might agree to a delay, but I would view a last-minute request to reschedule as reflecting negatively on the candidate. The only exception would be a serious medical problem or other family emergency.
Note: I work in a formal work environment. Other companies may be more understanding under a wider range of circumstances.