What’s the maximum length a TrueView video ad can be?
1 minute, 30 seconds
There isn’t a time limit
There is no limit on skippable in-stream ads, but YouTube recommends using videos that are less than 3 minutes long.
You can also run videos longer than 30 seconds. You can try longer product demos, customer testimonials, or a how-to video demonstrating your product in action. But you will be charged if a viewer watches 30 seconds of your video (or the duration if it’s shorter than 30 seconds) or interacts with your video, whichever comes first.
Read more here: //support.google.com/adwords/answer/2375464?hl=en