Not sure I understand. Both are an overlay blocking content. I suspect Google would still punish an interstitial overlay with a countdown timer that dismissed it. If you don't click, YouTube sometimes makes you watch 30+ seconds of ads.
To be honest I've seen a couple advertisements that I watched the full ~5 minutes. Both were game trailers that were really interesting. I would have rather had a "click here to view the actual trailer video instead of the ad version" button though. I was sold after the first 2 minutes, but couldn't see the full name of the game until the end.
Over 95% of the stuff I watch on Youtube is gameplays, collagehumor and tech reviews, yet all my ads are diapers or clothing softeners. I've no idea why their algorithm sucks so much for my account.
Here's Google's post about it: https://webmasters.googleblog.com/2016/08/helping-users-easi...