Throughout the battles of Yggdra Union, time passes in the form of day cycles. There are three (3) day segments: Noon, Evening, and Night. Some classes, such as Hunter and Assassin, become exceedingly powerful during a particular time of day; there are also equippable items that grant such an advantage (ex: Straw Hat). There are instances throughout YU in which the daytime is fixed. Furthermore, frozen rivers will thaw when the day cycles to Noon; be very cautious not to have any non-Undine units positioned on ice before this occurs, else the unit will drown and Zero Reset. Frozen rivers will not defrost if the map is fixed at Noon, however, presumably because thawing only happens when the cycle changes from Night to Noon.