On the 744 with GE engines, nacelle anti-ice is now used in the descent whenever the temp is <10C and visible moisture or other icing conditions exist or "are anticipated." There is no requirement for a specific time before entering those conditions, but if descending through multiple cloud layers, it is smart to turn it on at TOD and adjust the VNAV Descent page prior to that time so the correct TOD is calculated for the higher idle N1.