Retime visibility
Retiming operations act on all layer parameters, including its visibility keys. Applying a Speed Multiplier with a value of 2 will reduce a layer’s presence on screen by half.
However, it’s possible to make an exception for this particular type of keyframe in order to keep the same visibility on screen. This comes in handy when keyframes are placed according a specific rhythm or for specific moments of an animation.
To do so, uncheck the Retime Visibility option, which is checked by default:
Here you can adjust the Speed Multiplier and see what happens in the Dope Sheet when this option is checked/unchecked: