If your flight is at 5:20 a.m., then you'll be at the airport and going through security somewhere around 4:30 a.m. Be prepared that not everything will be open.

I'm not sure how it is in DFW but other airports I've been through at odd hours have shut down certain less-used security checkpoints and herded people toward main ones. Also, coffee was hard to find! Hopefully that won't be the case for you.