It depends on the exchange that you are using. They may have an option for some very fast bank transfers but usually at a high fee. Unfortunately most exchanges don't offer such an option and the fastest ones take at least 1 business day.

However the fastest way may be to sell Bitcoin directly to another person in cash and then deposit the cash into your bank account. You can check https://localbitcoins.com/ to see if there is anyone near your location who you can sell Bitcoin to for cash in person.