That's one of YouTube's anti-adblocking measures. As far as I know, it only happens on a “cold” load (like when opening a YouTube video by going to its URI directly). You can avoid it by navigating to it from within the YT interface.

Funnily enough, the time you have to wait is still shorter than the ad you would've had to watch.

I quoted GLaDOS saying “Don't press that button. You don't know what you're doing.”

… and no one pressed the button. It ended.