“…Fox‘s real-time drama ’24’ which will again kick off its season with four episodes screening on two consecutive nights… The fifth season will premiere with two episodes from 8-10 p.m. January 8, followed by two from 8-10 p.m. January 9 (the second episode January 9 will be the show‘s 100th). On January 16, the fifth hour of “24” will air in the show‘s regular 9 p.m. Monday slot.
The scheduling strategy is designed to let viewers watch an entire season on a weekly basis without repeats or pre-emptions…”
Confimation their that Day Five will kick off in the same way that Day Four did, and that helped in achieve the highest ratings of any series. Link to the original article is below, but be warned, contains major spoilers regarding casting details some may wish to avoid.