I recall reading somewhere that less than 5 years is the average time it takes for most individual works to earn the majority of its value, tapering off from there
So I’d probably do a 2-tier system:
Tier 1: independent civilians. After 5 years any normal civvie can take your work and use it without your permission to do whatever they want with it
Tier 2: Companies. Life of the author. For as long as the original creator is alive no company can ever use their work without permission