Originally Posted by ATOBTTR

You should be able to open the App and select Preferred seats as soon as the reservation is made. There's a nice glitch in the DL App that allows you to select Comfort Plus and Preferred seats even when the reservation isn't ticketed. DL.com will catch it. But through the App you can get what you want. I do this regularly for the gov't fares I regularly fly on which don't ticket until a few days before departure.