Looks like YouTube is already detecting this or has some logic to detect that the ads were played at a different speed.

Try moving through a video when this extension is active and you can see that the advertisement is getting active for almost every possible forward / reverse time selection on the video timeline.

It is just too many blank screens and though it saves a couple of seconds in the actual advertisement watching space, it does provide an unpleasant experience of watching the black screen for a few seconds.

I can live with that (and most should be!), but wanted to record this observation so that it get's to the developer's attention for improvements (if possible!)

Hope it helps.