While coding, I tried to create a PotionEffect using PotionEffectType.createEffect method.
I inserted the duration, and the duration didn't work.
When I inserted 100 (ticks = 5 seconds), It worked for a bit longer than 1 second, and when I inserted 500 it worked for a bit longer than 5 seconds.

After some testing, I tried creating the effect with the potioneffect constructor and entered 100 ticks, it worked for 100 ticks.

Basically, durations in createEfefct method don't work correctly.