With the following code...

entity.addPotionEffect(PotionEffectType.SPEED.createEffect(100,0));

the effect should last for 5 seconds, but instead, it lasts for hardly one. When this is called in an EntityDamageByEntityEvent (only place I've tested) the potion effect duration is bugged. During testing, I have found values of around 800 give 9 seconds which makes no sense as 20 ticks are in a second. 

Now, I have worked around this by creating a PotionEffect with new PotionEffect() instead, outside the event. This works fine if I have this stored elsewhere and use it when adding a potion effect. Make sure to fix this or give documentation as people such as I can waste several amounts of time trying to debug this. 

Thank you