Yup what they said. On NW it DID matter and in-fact there were some creative ways to check-in and still get an EUA but not on DL. The process is much cleaner on DL and when you do check-in you will be slotted in line for the battlefield upgrade based on fare class (also did not matter on NW), status, and time of UG request, so essentially booking. You can check in 1 hour prior to departure and if you qualify you will be number one on the list. I like the DL method but I do worry that the focus on fare class could easily lead to reduction in upgradeable fares where NW took that out of the criteria (other than "Full fare" Y) and went with time of ticketing as well as check-in time which are fare class independent.