As said previously in this thread countless times, people have low attention spans. If you want people to buy your product, they need to know about it in a short amount of time.
Marketing 101
that's not some golden rule, dont know how much marketing experience you have lol
it depends on your hook and the quality of the content. if i enjoy what i'm watching, the time it goes for is pretty much irrelevant (within reason obviously). sure, if you've got no hook and the video is stuff, then start looking at the length but otherwise quality should be the driver here
edit: also worth noting that people looking to purchase some generic "product" have very different motivators from people looking to purchase a game for entertainment. it's not a compatible brown townogy