Little is known about the game. The single piece of art featured in the magazine depicts a girl looking out over a ruined city from a clock tower. As translated, Ishii explained that the game has "the theme of the calamity that has become a trauma within me." Ishii is from Nishinomiya, a city affected by the Great Hanshin earthquake of 1995.
As mysterious as Time Travelers may be, even less is known about the platform its being developed for. Hino said that the game is "centered on hardware that's not yet in this world; [and] it will expand to other hardware." It does seem appropriate that a game about time travel would be announced for a platform that doesn't exist yet.
Considering Level-5's success on the DS, we'd guess Time Travelers is in development for 3DS, though it could also be designed for Project Natal or PlayStation Move --- or even a platform that's yet to be revealed. How great would a 3D game called Time Travelers be, though?