I am very patient. It is rare that I won't sit through an entire Kickstarter video, even if it's 10 minutes long (and I've seen some that are), but maybe that's because as a friendly Creator, I know how hard it is to put a Kickstarter together correctly. And I want them to do well and hope the video gets better and want the best for them, to honor their efforts. That said, the more Kickstarter videos I see, the more I notice mistakes in them, and the less patience I have. Even so, I still generally watch till the end (and I value my time more highly than money).
Another way to think of your video is statistically. Out of every 10 people, how many of them do you want and expect to sit through your whole video? Do you care if they watch it all the way to the end? Are you planning on putting any important information at the end? Every Kickstarter Creator can tell you about how many people actually watched their video to completion and I can tell you that it's not many, sadly.
My video was originally 3.5 minutes long. I worked extremely hard on it and was very happy with it overall. I showed it off to some people and they were giving me a hard time saying they'd never watch one that long. In fact, some of them said they don't watch the Kickstarter videos at all. They ignore them or get annoyed or bored with Kickstarter videos after about 10 seconds, unless it is extremely well made and pertains to their interests. I was encouraged to cut it down to 1.5 minutes long, which I did (and yeah, that was very hard).
Case in point: I have a live anthology
Kickstarter right now (someone pledge, please! we're sitting at 40%) and I can look at my Kickstarter Analytics and see that only 34% of the people that hit play watched the video till the end (out of 251 people thus far). I've heard around 24% from another Creator and around 30% from yet another and suspect that most Kickstarters are seeing such low numbers. Of course if you don't have many backers and a lot of family members go on there, that twists the result as they may not care about your video so much as how to back you, so take everything with a grain of salt, but your best bet is to make a short video around 1.5 minutes long, IMO. And that's what I'm hearing a lot, so my guess is that a lot of Creators noticed the issue with potential backers not watching all the way through. Anyway, good luck with your Kickstarters, folks!