If you are not checking bags and are able to print your boarding pass before hand, 4am is more than enough (I have done 430-445). The reason for long lines/crowded is due to morning rush hour--only 1 runway for 8-10 domestic flights between the 545 and 615am time slot and 3-5 international deps/arrivals (see airport website). But, if checking bags, shoot for a time between 330-4. Good luck!