One month.

如果簽證延期沒批的話， 多久就要離境，算不算逾期居留？ 對下次簽證有沒有影響？

-When the B2 extension is denied, you are out of status immedaitely if your original I-94 expires before the denial. You can leave US in one month and noramlly it will not affect your future visa application.