It don't make sense how it work in CK2 in which character opinion from stuff stay at a certain value for a certain time Before is removed completely. A more natural way would make it work like country relations in EUIV in which opinion modifiers decline a certain amount each year and eventually disappear. Like if you give a gift in CK2 it is maybe 30 opinion for 5 years and once the gift is over the opinion jump from +30 to 0 instantly. How it could be is that 6 opinion Points is lost each year from the gift which would mean opinion go from +30 to +24 to eventually +6 and the next year 0 which would feel more natural.