Paint Bucket Mask not working with keyframes

Hello,

I'm trying to highlight part of a map in premiere pro, using the paint bucket effect and a mask that highlights a certain area.

I want the mask to fade in and out, so I have 3 keyframes. One with mask opacity Zero, two seconds later mask opacity 100%, 2 seconds later, back to zero.

It isn't working, it doesnt change when I play the sequence or export video. Can someone help please?