NEW YORK: Even ten-second video ads may be too long for the millennial users of Snapchat, as evidence has emerged of 70% of them moving on after just three seconds.

"It is a very steep, rapid decline for the brand [after three seconds]," explained a top executive at the agency, who shared a chart with Digiday showing how Snapchat ads had performed for one client.

"[W]hen marketers think they are buying a ten-second ad, they really have to get their message out in two seconds, or else most won't see it," he said.

That may be a comment on the quality of the ad, however, as much as on the attention span of the target audience. "Completion rates for Snapchat vary depending on the creativity of the ad," according to Jeff Lucas, head of sales and marketing at Viacom Media Networks, a Snapchat partner.

"Most brands that try to be native, organic to the platform, have higher completion rates," he added.

Some advertisers claim an average view time of four seconds, with a completion rate of 34%.

And one source reported that researcher Millward Brown had measured favourability lifts of 50% or more among those exposed to certain ads run during the Snapchat Live Story for the MTV Video Music Awards compared to those not exposed.

Lucas also pointed out that, regardless of how long people actually viewed ads on Snapchat, there were other benefits to using the platform.

"Snapchat is where ads are pure, 100% in view of the screen, not hidden anywhere," he said. "That's a lot better than advertisers totally paying for things no one is ever seeing."

Last month Digiday reported that Snapchat was charging advertisers for "zero-second video views", with brands paying every time an ad loaded. But advertisers aren't charged if a user chooses to skip an ad before it loads.

Data sourced from Digiday; additional content by Warc staff