dont know when this exactly happened or if it was fixed in the last update(got other mods in my modpack that arent yet compatible with latest fabric API), but the onset delay could be bugged for the level 4 enchantment.
was testing it a bit and noticed a weird jump from full set level 1-full set level 2-full set level 3-full set level 4(all tested with leather armor incase the armor quality had an effect on it).
this weird jump being the duration of onset delay, this being 30s-60s-90s-1200s

Hi. This is not a bug, per se, it's just a very badly balanced formula. ;)
I'll mark this as a feature request though, because I feel like this requires a change as well.