I speak from zero experience of selling, but a great deal of experience of public speaking ...
What really, really matters is seeing something interesting early. Really early. First 3 seconds maximum. And not generically interesting - interesting specifically to a person who will give you money.
If they won't give you money, you don't care.
So who will give you money? Figure out who they are, and make sure they see something they want within 3 seconds.
Beter yet - 1 second. Hard to achieve. Be creative.
But to some extent, that's the point. I've outlined a suggestion for what you're trying to achieve at the next level down. It's now your job to think creatively to find a way to do it (assuming you think it's right).
If you succeed then you're doing better than your competitors, for I've rarely seen it done at all.
Also, assume some viewers will have their sound muted. Assume some others will switch to another tab and only listen to it.
http://wistia.com/blog/does-length-matter-it-does-for-video/
Bottom line, keep it as short and as punchy as possible.
As in writing, editing is king. Remove bits.