Recently, I have been told that the seats release 4 hours before flight time. However, on more popular routes (LGA-ORD), the seats will not be released until flight time.

In terms of getting on the list, in general, you have to wait until you get to the airport (in this case, DFW). However, I have been told that certain supervisors can put you on the DM list at your originating airport.

--Jim