Will a large delay before these interstitials appear change the impact on a pages ranking?
JOHN MEULLER (Webmaster Analyst from Google):
It sounds like you’re trying to be sneaky and showing an interstitial, even though we’re saying that this is a bad user experience. So I would be cautious there with regards to just trying to gain the interstitial algorithm. If there’s a legal reason for you to show these interstitials, then fine. Of course, you can show them. Otherwise, I would try to find different ways to grab the user’s attention when they’re looking at your pages.