If you summon an Area Effect Cloud, it waits 6 ticks before applying your effect even if WaitTime is 0.

Example command:

/summon area_effect_cloud ~ ~ ~ {Radius:4f,Duration:1,WaitTime:0,Effects:[

{Id:8b,Amplifier:12b,Duration:80,ShowParticles:0b}

 

 

But if you change your Duration to 6:

/summon area_effect_cloud ~ ~ ~ {Radius:4f,Duration:1,WaitTime:0,Effects:[

{Id:8b,Amplifier:12b,Duration:80,ShowParticles:0b}

 

 

Then it works just fine.