Automating a mask on/off in fusion

Hi,
In addition to the mask moving using automation with keyframes, I'd like to disable/enable the mask altogether at some point in the timeline.
For example, I want the mask off at 00:00, then on at 00:20, then off again at 00:40.
How can this be done? Thanks.

I assume you have a mask node for this.
In the inspector window for the mask node you will find the control "Level" (I think it is even the first entry).
Right click on the label, not the slider or number, but the label, and select "Animate".
Now you have the little diamond on the side of it to create keyframes for the level of the mask.
You can further refine this in the "keyframes" panel.

If you have further questions, please ask.