How early can you check in for JetBlue flight? 24 hours before their departure, JetBlue customers can check in online. If your flight is scheduled to depart at 2:00 PM, you can check in online starting at 2:00 PM the day before your trip. The JetBlue mobile app allows you to check in, select your seat, and obtain your boarding pass. Do not forget to complete your online check-in before the window closes at 30 minutes prior to departure.

https://www.airfleetrating.com/check-in/jetblue-check-in-policy/