Hello,
Yes, if you fail in one subject in the CHSE annual exam , you can appear for the instant exam , which is usually conducted one month after the result.
If you appear for the instant exam, your result will be under the ex-regular category, not the regular one. The exact result date will depend on the board's schedule.
Hope it helps !
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile