How to make BLine appear in specific keyframes ONLY

I want to make a BLine appear only after specific keyframes, then disappear from the animation after specific keyframes.

For instances, I want my character to grab a book out of a box and read it.

The character is an encapsulation of many BLines. No problem. The box is another simple BLine. The book is another simple BLine.

I want the book to appear after a certain point in the animation. I know that I can hide it behind the box and bring it out. That’s the only option that I know of. Is there is another way, I’d like to know about it.
If I create the book BLine on frame 400 of the animation, then the book BLine will appear on all the frames prior to 400 after I export the animation another time. How can I control the appearance of BLines so that they only appear on the frames that I want them to appear on? I can use some advice, thanks.

BLines (now called Splines), like any other layer can change its visibility by the ‘Amount’ parameter.
Making it zero (full transparent) will make it disappear and changing it to 1.0 will make it appear again. Any value between 0.0 and 1.0 will make it partially transparent visible.

You can use ‘Constant’ interpolation to quickly change between one value to other without transition (which maybe is what you’re looking for).

Is the “amount” parameter keyframable?

All the layer parameters are “keyframeable” :mrgreen: