A Time Band was a device created by the Batman during the time of the End Future. Through direct manipulation of Mother Box technology, Batman was able to change the Boom Tube technology. Instead of going teleporting to another location while time went by at a constant pace, the Time Band instead sent the host back in time. The Time Band operated in jumps, posed the danger of being vaporized and could only send it's user back in time to an accurate date depending on the mass the person going back in time.
Given that the amount of chronal energy the Time Band manipulated was massive, it took an even larger amount of energy to power a single jump in the band. When originally created, there was only enough energy for one jump, which was repowered by Madison Payne, although it drained her of her Firestorm abilities. Another being powerful enough to power the Time Band was Brother Eye, the extremely powerful AI the Time Band was created to destroy.