IME it depends on the size of the aircraft. For domestic flights, 753 and bigger usually boards at T-40, 752/A321/or 739 boards at T-35, 738/A320 and smaller usually at T-30.
Originally Posted by
FlyinHawaiian
Boarding times will be displayed on your boarding passes. If you use Delta's mobile app and set push notifications for your flight(s), you will also be sent a pop-up message when boarding starts.
The DL app or paper BP will always show boarding at 40 mins prior to departure.